Here I repost a lengthy diatribe about homelessness and begging that I posted to hssst's journal as a comment.
Sometimes people need money for something other than food. There's plenty of leaches out there who just turn begging into a lifestyle/career. But you never know the circumstances.
Maybe they have psychological problems and our society has turned it's back on helping them directly. So they can't hold down a job, they can't behave rationally or consistently enough to do anything other than go into basic survival mode, begging for money on the street.
Maybe they are trapped in a situation where because of the employment situation and the welfare situation they've been unemployed for so long that they can't collect and unemployment, they can't collect wellfare, and they can't get a job because their employment history has huge gaps and with everyone looking for work there's always someone more qualified than them.
Maybe they're just going to take your money and spend it on booze and drugs. But maybe that's all they've got. Maybe they're horribly addicted. Maybe they can't hold down work because of their addiction. But maybe they couldn't hold down work before they got their addiction and so they turned to this for an escape. Maybe they can't afford or don't understand rehab. Maybe a little booze helps them to fall asleep where they have no bed, no safety, no warmth, no quiet, no darkness.
Maybe they have some dietary problems and have to watch what they eat. Maybe they're afraid someone will try to poison them (either because they are paranoid schizophrenics or because there really are anti-homeless vigilante psychos who would hand out poisoned food) if they don't get food straight from a vendor.
Most of these people, regardless of their circumstance, whether they are con artists or whether they are legitimately fucked by life, will lie to you. No one wants to give money to people with a simple story "I'm mentally ill and can't keep a job", "I'm an ex-convict and can't keep a job", "I'm a shell-shocked veteran and can't keep a job", "I'm a heroin addict and can't keep a job". People give more money for complex sob stories so all beggars learn to be con artists, whether they started that way or not. I try not to analyze the stories.
I figure out in advance how much "street tax" I can pay and I pay it. Some days I can't pay any and I politely say I don't have any money to give and am generally left alone.
Anyway, I give money when I can. Mostly, I give more money when I'm traveling though. It's hard to afford giving money to the person that you see EVERY DAY when you go to work.
Ironically, I got the distinct impression that Chicago people were much more tolerant of the homeless than Los Angeles people. In Los Angeles the cops sweep the homeless off the streets every morning and truck them to the outskirts of town. You don't see beggars (not even street musicians busking, which Chicago downright embraces and encourages) at all. The sidewalks near buildings are all purposely built on a slant so that you can't sleep on them without rolling down into the middle of the walkway. LA is agressively anti-homeless whereas Chicago seems much more tolerant, even if grumpily so. Chicago people peacefully coexist with the homeless population even if they bitch and moan about them.