A few times in the past I've given rides to homeless guys or cash to them, sometimes just conversation even if that's what they're after. At the end of the day it's not like I'm doing volunteer work, but treating any homeless person who approaches me with the same respect I would anyone else has so far left me unharmed and even helped--I've had homeless people help me change tires, for instance. I get the feeling that even with the damage to your mind that the stress of homeless can do, people are still people and people like to feel useful and respected.