The long term solution (getting someone off the streets) is irrelevant for most homeless people. They're homeless now. What might be done to fix their situation in the future isn't something they spend much time thinking about. Unless you have a way to get someone of the streets right there and then, giving them money is by far the best thing you can do.
Is getting people off the street and helping them lead productive lives not the aim of many charities? I prefer to give to them (and for them to use their judgement) than whoever I randomly find on the street.
