Some people deserve to die
You might not agree, but certainly a large number of people think this way. Where the draw the line is a very personal choice, but there's still a line. Example. This person abducted and killed four girls, aged from 4 to 7, in his car before dismembering them and molesting their corpses. He also engaged in cannibalism, preserved body parts as trophies, and taunted the families of his victims. Do you think he deserves to die? Do you think he deserves to die even if you must die with him?
Some people will recognize that answering the latter question with 'yes' is drastic, but feel like they should do it anyway. When the other personRemember, you're dealing with someone who is willing to kill you. Given that they are willing to kill you, should you be willing to kill him/her? What if they've already wounded you? Maybe you'll say "I don't care", but then the world ends up being repopulated by the children of people you consider despicable, so not everyone might consider that an improvement.
Here's another example. The question-asker originally wrote that the Russians deserve to die, so in the event of a Russian nuclear strike, he/she would probably approve of retaliating. Here's PutinRussian state television host Dmitry Kiselyov saying something similar. “Why do we need a world if Russia is not in it?” If you take him at face value, then in the event of a NATO nuclear strike, he will also retaliateapprove retaliation.