In the Star Wars prequel trilogy (and in the Clone Wars TV show) we see that Darth Sidious fooled the galaxy gradually.
The Republic was reorganized into the Galactic Empire with the people's consent, Palpatine having convinced them that the Jedi were traitors. Aside from a small group of perceptive individuals (like Padme, Bail Organa, and Mon Mothma), we get the impression that during the reign of the Empire the average person (citizen or officer) might believe that the Empire was in the right.
Consider the fact that:
the Emperor was careful to conceal his identity as a Sith
the Emperor kept the Imperial Senate intact for a while
Tarkin seemed to discourage Vader from choking imperial officers
It seems as though the Emperor needed to keep up appearances of being good and wanted the imperials to believe that as well.
However the Empire has some really evil names like Death Star and Star Destroyer that would likely tip people off that the Empire was evil.
I realize that the construction (as well as probably the name) of the Death Star was kept secret before it's completion. Star Destroyers, however, were plentiful before that.
###Did the average imperials (such as stormtroopers, officers, or admirals) know that they were the "bad guys"? #If they don't consider the Empire to be evil, then how can they justify the Empire's action to themselves?