Memes

There are definitely some like that. The American system has a number of tricks to try to force people to do what they like as well though. Poverty, over policing of minorities, lack of social safety nets etc can cause people who grew up barely avoiding prison choosing military thinking the only choices they have are death or military, shoved at them when they're too young to really know the world. Add education that specifically avoids or lies about what US actually does overseas, plus a bunch of jingoistic propaganda making being a soldier appear to be a respectable profession.

I grew up in a cult that avoided military so I never had those feelings myself, so I got to watch it from the outside, and even the pledge of allegiance every morning was weird jingoistic programming from early ages. It can be difficult to see past that at 17. I'm not saying they don't deserve any punishment, but I do disagree with the idea that every single one wanted to kill people.