Artists can do that because they have license to do so. Even under commission, you are entitled to do things however you want.
However, being flat-out rude and putting words into people's mouths does you no good, and even when you compare the two evils, yours is still the greater.
You know, advanced studies have shown that besides the risk of irresponsible spending, giving money to a homeless person will hurt them more than benefit them.
Reason why? They will be forced to live through more hardship because of a prolonged life. Am I saying that because I hate/discriminate against homeless people? No. The best thing to do is encourage them to join some kind of a promotional program.