Then they're busking, people have made a living doing that since at least medieval times.

Fact is, working for your money is effective even if you're begging. People are more likely to toss a dollar to a guy with a guitar or some other gimmick than they will to somebody just sitting there with a sign. Is it cruel, or gross? Maybe, yeah, a little bit. Extra sucks for the disabled homeless, I do understand that. But being a street performer is a legitimate job in some places. People will pay money for entertainment whether you're on TV or on the corner of 5th and MLK. If a homeless person wants to dance for a dollar I say let them. Begging for spare change is legitimately a competitive business. That can make the difference between getting food and a haircut or not.