We see that in DS9 the Bajoran religion is alive and kicking, but I've never seen any mention of a religion that came from Earth, or one practiced by humans.
Are any of Earth's religions still practiced in the current setting for Star Trek in the 23rd 24th century, or have they all died out? If they have 'died out', is this ever mentioned?
I can't give you a page or a reference or link, but I can tell you this was told to me by Ronald D. Moore, under a professional situation.
When I was pitching to Star Trek: The Next Generation I had a couple stories that dealt with the effects on the Enterprise crew due to the religious beliefs of other beings. In one case, I had a story I pitched about an off-shoot of the Betazoid race I temporarily called the Gammazoids who were very religious and superstitious and considered Troi, for several reasons, an abomination.
Ron's response was that something to the effect that (and this is NOT an exact quote), "In Gene Roddenberry's universe, people will have outgrown religion and the problems it causes and live without the need for it." There was a little more to it than that, but that summarizes it. Now, remember, Ron went on to do Battlestar Galactica and has shown he sees the importance of religion as a motivating factor in human behavior. I think that shows he was not talking about his views as a writer, but was speaking specifically of the "rules" of the Trek universe.
Roddenberry did not have a kind view of religion and on that story pitch (and one other) Ron was clear to draw that line and say there was no religion -- not only for our characters, but for other species as well. Roddenberry wanted a universe devoid of religion.
However, in Star Trek (the original), we do see in Balance of Terror there is a ship's chapel, but we see it used for a wedding service and we don't see any hint of it being used for worship. We do see, in Bread and Circuses, a parallel Earth where Rome never fell and Christianity is just starting to spread in their equivalent of our 20th century, but none of the crew members on the Enterprise claim any affiliation with Christianity when religion is discussed.
But before anyone gets going on Sto-vo-kor or anything else like that, I'll point out that I was pitching before Gene Roddenberry died, and for reference, he died just about the time Unification, Part I aired. Note that after Roddenberry's death, we did learn about some Klingon beliefs (including Sto-vo-kor) and we also saw, in Deep Space Nine that the Bajoran religious beliefs played a major part of the storylines and, as pointed out in the other answer, Chakotay's Native American spiritual beliefs were referenced in Voyager.
So, while Gene Roddenberry didn't want religion as a part of, at least, Star Trek: The Next Generation, it was discussed in one episode of the original series and there was a ship's chapel (which we only saw used for a wedding). We also see that after Roddenberry died, while Earth religions were avoided, religion did start to enter into the storylines after Roddenberry's death.
Religious belief/observance was clearly NOT widely practiced, and was negatively viewed by many.
Picard exibited typically strong atheism - exhibited for example in TNG: "Who Watches The Watchers"; I'd call it "militant atheism" - he refers to religion in pretty strong negative terms:
"Horrifying... Dr. Barron, your report describes how rational these people are. Millennia ago, they abandoned their belief in the supernatural. Now you are asking me to sabotage that achievement, to send them back into the dark ages of superstition and ignorance and fear? No!"
The reasoning behind that is pretty clearly explained in Tango's excellent answer.
But there were some minor indications that religion was not 100% dead:
They had Christmas celebrations
n 2266, a Christmas party was held for personnel in the science labs of the Federation starship Enterprise. Captain James T. Kirk made an appearance, and ended up spending a romantic evening with Helen Noel after they met, danced and he talked about the stars. (TOS: "Dagger of the Mind")
Religious elements in weddings
At her wedding, phaser specialist Angela Martine genuflected toward the altar of the ship's chapel, (TOS: "Balance of Terror")
In DS9: "Penumbra", Kasidy Yates mentions that her mother would prefer her to be married by a minister.
If you include non-canon (novels), there was at least one Rabbi mentioned:
David Gold, captain of the USS da Vinci and his wife, Rabbi Rachel Filman, in the Star Trek: Starfleet Corps of Engineers series identify as Jewish, as do their descendants.
In 22d century, Dr. Phlox observs Buddhist monks in a monastery (ENT: "Cold Front")
Kirk has said "mankind has no need for Gods. We find the one quite adequate." (TOS: "Who Mourns for Adonais?")
More details can be gleaned from the links at Human Religion@Memory Alpha
There are hints throughout the various Star Trek series that religion amongst the Federation worlds is not dead. Indeed, Vulcan as an example has a very strong religious base that is referred to on numerous occasions. As far as earth religions specifically, it has been left quite vague in most instances. The most notable exception I think is Chakotay on Voyager. His native American faith is addressed on multiple occasions, whether you would consider that a religion or not. I can't imagine that it would be the only example of a belief system that survived into the future.
I think this is likely intentional. The two topics that people seem to be the most passionate about are religion and politics and Star Trek would often go out of its way to avoid tackling either one on more than a high level. This despite the fact that they address so many other social issues of the world.
However, I've never seen any canon that directly addresses the question one way or the other.
Data mentions "a celebration of the Hindu Festival of Lights" in Data's Day implying that Hinduism is continuing.
However, Christianity does not seem to be faring so well. Katherine Pulaski says, "For much of the history of mankind, the breaking of bread was a sign of friendship and community. Something we have gotten away from in the twenty-fourth century.", in Time Squared.
Perceptive people will realise her knowledge of the purpose of the breaking of bread wasn't that hot, either.
I think any assessment of the status of Earth religion in the Star Trek universe is at best speculative. Note that we almost never see people in a civilian context in these shows; rather we see Starfleet personnel, usually on duty aboard a starship. The behavior of people on a travelling vessel under discipline of a chain of command is much more constrained than that of civilians - particularly since we nearly always see them on duty, and assigned duties necessarily take priority over personal religious observances [yes, DS9 is looser, but it is still Starfleet]. I'll bet if you naively observed behavior on, say, a typical aircraft carrier, you might conclude that religion there is dead, too.
I found this reference and then searched the answers here and found that @DVK already mentioned it. But I don't believe his focus is correct since he calls it a 'minor indication religion is not 100% dead'.
In DS9 "Penumbra" there is this exchange:
SISKO: No, I know. What do you say we have Bill Ross to perform the ceremony?
KASIDY: My mother would prefer for her daughter to be married by a minister. But an Admiral's the next best thing.
I don't see how you can take that as anything but a strict indication that Kasidy's mother adheres to a religion and that that (implicitly Christian) faith still exists.
I consider this to be an explicit answer to the question.
In "The Corbomite Maneuver", the alien gives the Enterprise crew 10 minutes to pray to their deity or deities before the ship is supposed to be destroyed and not one crew member even considers it. I think that says it all.
There are two kinds of religions that can be seen in the 24th century of Star Trek: those of dogma, and those of culture. Earth and humans of the 24th Century Star Trek Universe show some traces of cultural religion, but dogmatic religion is not shown to have any widespread adherence, presumably because the advance of human knowledge has shone lights further into the corners of the unknown. However, some mythical religious elements are presented as being factual and thus could be followed by a dogmatic element. In Who Mourns for Adonis the Enterprise encounters a planet on which the original Greek gods from Mount Olympus on Earth have moved, sans worshipers. These "gods" are revealed to be merely sufficiently advance beings. In Bread and Circuses the Enterprise encounters a religions which turns out to be be very similar to Christianity (Uhura's notable "son of man" quote). The native population is not human, but humans from a lost starship are on the planet and have interfered with the planet's natural evolution.
All of the remaining dogmatic religions in Star Trek still exist because they can compete or even out-compete 24th century technology. The Bajorans revere or worship the Prophets aka wormhole aliens because they are real highly advanced beings which exist outside linear time and which have interacted with the Bajor for at least ten thousand years. The Vorta consider and treat the Founders as gods because they were genetically programmed to do so. The inhabitants of Rubicon III have a rule based interaction with their deity, again another highly advanced being. Conversely, the Klingon gods appear to be a mixture of dogmatic and cultural. Worf states that they were killed millenia ago because they were "more trouble than they were worth" but the reality of Sto-vo-kor is presented as partially as cultural (a place for worth for warriors who die in battle) and partially dogmatic, while in Barge of the Dead the question of how real the events B'Elanna experienced is left very open for interpretation.
Now what does all this have to do with Earth religion? In The Chase we learn that many humanoid worlds in the galaxy were seeded. Humanoid races throughout the galaxy thus share common DNA and programming, and thus similar tendencies would play out towards religion, which in primitive societies had a big role in explaining the unknown. The very premise of Star Trek is boldly going into the unknown in a manner very incompatible in many ways with religion. Kirk, Picard, and Janeway did not cower in the face of advanced beings - and there were many. They did not worship them or seek to placate them, nor did they have any interest in forming any kind of "fan clubs" to any individual. Instead, they sought to learn from these encounters. I think Deep Space 9 portrayed this best, where human captain Benjamin Sisko spends seven years coming to the realization that he plays a vital role in the events of an actual valid religion. Along the way he responds to his son's question about whether the entities of the Bajoran religion are "prophets" or "wormhole aliens" basically replying, "Why not both?"
Dr. Phlox says that he attended mass at St. Peter's in Rome (ENT: "Cold Front"). So Catholicism still exists at that time.
Also, in the animated series, Spock goes back to Vulcan to "honor our gods" as he puts it (TAS: "Yesteryear").
There must be earth religion still around in the Trek Universe. Here's why:
1) In the TNG episode: Sub Rosa, the funeral most obviously has Christian design to it and is obviously just outside an old church, built by the colony.
2) Dr. Phlox mentions observing Tibetan Monks in their monastery, and attending Mass at St. Peter's Basilica in Rome.
3) Christmas is obviously still celebrated as seen in many episodes/scenes in TOS and in the Nexus scene when Picard first arrives in Generations.
4) Kirk mentions, in the TOS, when they defeat the deity-being, that "mankind has no need for gods. We are adequate with the One".
5) In the Kirk-era film Star Trek V, Sybok clearly states that "God does exist. He has many names." and that "Heaven exists. The Vulcans call it Sh-Ka-Ree."
6) A ship's chapel is seen in TOS several times throughout the series.
7) In DS9: The Ship, the Catholic holiday of Carnival is still obviously observed.
8) Amazing Grace is played on the bagpipes at Spock's funeral by Scotty in Star Trek IV.
9) The Biblical book of Genesis is the reference point behind the Genesis Project, the rapid creation of life from nothing (that ultimately failed and was mothballed by the Federation as a result).
10) TOS: The Way to Eden, a group of fanatics believe in the Biblical teachings of the Garden of Eden and believe that it was never on Earth but actually another planet, and that they needed Kirk's ship to find it.
11) In various episodes/scenes in DS9, Voyager, and TNG, Jewish people are mentioned by name, seen in holodeck programs. Worf's adoptive parents' last name and background implies that they are Jewish.
12) The Vulcan salute (double V sign) is actually derived from a Jewish benediction hand sign.
So as you can see, religion, or at least MANY aspects of it survived into the 23/24 centuries. Granted, most religious texts of many of the world's modern religions clearly do not mention beings from other worlds, and most believe that Earth is the only planet in the universe with life on it. If beings from other planets were to land on Earth, I would think religion as a whole would die a very slow death. Probably religious wars would ensue, due to conflict among secularists who would want peace with the aliens, and religious elite who would want nothing to do with the aliens because it would threaten their positions of authority on the Earth.
Organized religion doesn't seem to exist on Earth in the 24th century, but many humans still have individual beliefs. Colonists might have carried earlier beliefs with them and passed them on to their descendants. Sisko says "There are things I believe in" when asked if humans believe in gods in one episode of DS9. In "Bread and Circuses," Uhuru says that the Roman officials were trying to denounce the "sun worshipping" religion in their broadcasts when she says they were talking about the Son of God, not the actual Sun, which Kirk reacts favorably to, saying wouldn't it be fascinating to see it all happen again, implying that the people they met were indeed parallels of early Christians. Of course, both the original and later series were products of their time, and while Roddenberry might have been agnostic at best being openly atheist might not have gone over as well with viewers or network executives in the 1960s.
Wikipedia has a listing of Jewish influences, practices, etc.: en.memory-alpha.org/wiki/Jew – JMFB 12 mins ago
We addressed some of your question about the Jewish religion at scifi.stackexchange.com/questions/32002/… I went into a bit more details than others did about it in my answer.
Chakotay practices a Native American religion.
Kirk mentions that we believe in one god. KIRK: Mankind has no need for gods. We find the one quite adequate. (TOS: Whom Gods Destroy)
In 2266, Doctor Leonard McCoy said, Lord, forgive me, before he killed the salt vampire. The doctor was saving the life of Captain James T. Kirk. (TOS: "The Man Trap")
TOS episode "The Ultimate Computer", the M5 computer credited God as a source of the illegality of murder, and Kirk later repeated that credit.
Why do people keep saying Roddenberry was atheist, religion has no place in ST, etc.? None of that is the relevant to the question and it's simply not true that there's no mention of earth religions or themes in ST. I'm not going to reiterate in detail what others have already stated about repeated mentions of Christmas celebrations, etc.
Just answer the question, the questioner simply wanted to know if there were still earth religions around, and what evidence there is of it. The answer is there are still earth religions around in the 24th century, and read those links to get some specific answers about one of them.
