I enlisted in 1998 while things were quiet. Clinton got us a nice raise back then. Then 9/11 happened and the military was inundated with right wing "patriots" reacting to events and looking to kill uppity brown people. I saw the quality of recruits diminish as the military lowered standards to surge troop strengths to engage in an illegal war. I recently met someone who was in my old unit only a few years ago and I didn't recognize the Marine Corps he described.
Personally, being ordered to partake in an illegal war in Iraq after having just left Afghanistan in an unresolved state only strengthened my liberal beliefs. Going to other parts of the world and seeing what politicians and superpower governments do to people, and the amount unnecessary pain and suffering that takes place at the hands of ideologues and dogma, should radicalize anybody against fascists and right wing ideology. People who see and experience all that and return even more hateful and bigoted are psychopaths.
I am proud of my service and my conduct in it, even if I don't agree with the missions I was on. I would do it all again. I loved being a Marine. The only people you'll find me hating are fascists and religious radicals. THAT'S who I learned to hate in the military because that is where most human suffering came from.
It surprises some people that I'm a liberal veteran. I tell them that you can't go through that and see all that and not be a liberal, not if you have a heart and brain.
And to anyone I piss off with this opinion: You're just telling on yourself.
I don't know about Army because I've always hated how shitty soldiers tended to be. Mouthing off to Sargents and being generally undisciplined pigs. Couldn't even follow a joint battle plan for a joint patrol and nearly got my convoy wasted by friendly fire. But PRIOR to 9/11 people like you describe wouldn't have made it through Marine boot camp if they didn't stop acting like that. I doubt they would have made it through USAF or USN basic/boot either. But army... yeah, probably went in and got his ass shot off.