I think everyone has to play a part. Government meddling in certain areas of life can be annoying and have a negative effect but I think in the case of homeless people there should be some involvement from the authorities. In an indirect way I think this is already happening. When a homeless person becomes sick or a public nuisance, police and medical people have to step in and that means public money has to be spent - here in the UK, not sure about the US or elsewhere - and that means the government antennae are activated for sure.
If there are too many homeless people this issue becomes political and then you'll see governments acting alright!
But private individuals and charities have to play a big role, and do, and carry out brilliant work on the streets and in shelters and what not. It's surely a sign of a civilised and compassionate society when the down and outs are at least given a chance to be rehabilitated and helped onto the ladder of progress.
I think all governments should have a responsible last resort department - when all else fails - a duty to help anyone who falls foul of the system. This has nothing to do with politics but more to do with humanitarian aid! After all, aren't governments supposed to reflect and represent the views of the majority - in a democracy at least - and the majority of people would always help to home someone and to keep them fed.
In the end we all have to keep helping those less fortunate than ourselves.