I think that food, water, and shelter is essential for everyone; that is what welfare and section 8 is for. If someone is on the streets begging, they are

A) already receiving welfare money and are trying to earn an extra buck. (I'd like to say for drugs, but that's judgemental.)
or
B) Not mentally stable enough to use the welfare resources.

Either way, I think we need to work more on getting to the source of the problem. Rather if is is mental care, drug and alcohol addiction treatment, leading them to a dr. to care for their disability, leading them to the welfare office to get help, job training, school, etc...