STFU, loser. I'll give them food, gas money, a lift to a nearby shelter, or just some friendly conversation, but I'll NEVER stoop so low as to insult someone for joining the military that serves my country.
You can say that it's for profit, that the military-industrial complex is ruining America, that we're scumbag imperialists, but you are the supreme idiot of all idiots if you think that the people you see on the streets were involved in ANY way whatsoever with U.S foreign military policy. Again, if you have an issue with anything we've done at anything militarily beyond individual unit-level actions, take it out on the people who actually MADE those decisions [high-level officers and politicians]. The vets on the street that we see? They were just chewed up and spit out by the system put in place by those in charge, a lifetime away from ever seeing how their system is actually working.
You want to help them? See if there's any way you can help your local VA. Otherwise, if you see a vet on the street and aren't going to do anything yourself about their plight, take a moment and appreciate the fact that they at least stepped up to do something they thought was right and assuredly was a monumental sacrifice, involving years of a lifestyle quite radically different than the one we civilians enjoy.