Part of the reason there are so many homeless in SF is because the SF government and local charities provide food and shelter. The tourists handing out money doesn't help with attracting them. Much of the panhandling money is used for drugs, as basic needs such as food and shelter are already covered by the government and nonprofits. If you really want to help them, volunteer at a homeless kitchen or directly donate to them.

I walk by the local drug dealers in the Tenderloin every day, and all the clientele I've seen are homeless people.