It's worth pointing out that where I live (a major east coast city) the vast majority of the homeless population seem to have drug, social and/or mental problems, ranging from obviously but mild to incredibly severe. Of course this data is somewhat anecdotal but I have enough friends who are social workers to feel relatively confident about it. There doesn't seem to be a large class of people making strategic plans to beg based on expected return.

For reference, I don't give money to beggars (due to concerns about how that money will be used), but I do try to give food to beggars, and I support tax money being used for public health projects. I guess this exposes me as someone who supports interventionist social policies in some cases.