I think the ex-military premise is wrong. Military folks have the discipline,, team skills, and intellect to be just who I would want around me in such a situation. It will be the street thugs, who are already parasites that would try something like that. They won’t last long around ex-military types.
I disagree. In a post-collapse world, ex-military (there will be no more "active duty" since there would be no gov't anymore) would be a problem for the same reason that all the ex-KGB guys who now make up the Russian mafia in the ex-Soviet Union are a problem.