Those guys aren't on food stamps because they aren't legal citizens. Most likely they are very recently off the boat, and working to pay back the smuggler who brought them in. When that's done they can start sending money home to bring the rest of their family over. Anyone remember indentured servitude? It's kind of like that.
They ride that way because that's probably how they(and everyone else) rode at home. And they aren't that hard to avoid as they never ride very fast and generally don't do anything erratic, even if they are on the sidewalk or against traffic.
G-unit is right about them giving other cyclists a bad name though. A few years back an old guy was hit and killed by a chinese food deliveryman riding on the sidewalk on the upper west side. That caused all kinds of problems for cyclists, especially messengers as the media/general population doesn't know the difference. I got at least two tickets in the month or so afterward. Not even redlight tickets, but dumb stuff like not having a bell or reflectors(thanks Rudy, you bastard).
But still, this poor guy didn't deserve to die. I see children doing stupid things on bikes all the time, do you think they have it coming as well?