I can't speak to the moral character of the average veteran grunt, and whether they are potentially amenable to revolutionary causes etc.

But the people who go to /r/army to post in that thread are evil nazi fucks, more openly genocidal than e.g. cops

I guess you probably could have deployed to Iraq and come back relatively normal and pretty jaded, disillusioned with at least the military. But if you were in Afghanistan your job was probably just to murder fifty people a month, that's why you were there.