The more people that just "go with the flow" the easier it is to do and the harder it is to be an individual. I would say something like groupthink or the bystander effect played a large role along with those guys being young and dumb.

I don't so much hate bums but pan handlers (and there is a huge difference). 3/4ths of the homeless are unmedicated schizo's and the medicine they take makes them feel "normal" so of course they stop taking it fairly regularly.