Why does this job need to be given only to homeless people? If they are paid less than a normal worker would be (and they are, since they aren't paid anything at all), I'd say this is profiteering off the poor.
Because they have the least chance to make money.
(Except the ones in Laguna Beach, CA which can make upwords of $100 a day just begging to tourists, which they throw away on alcohol nightly. The $100, not the tourists.)
Many moons ago, when I use to deliver pizza to a beach island resort on the east coast, I met a bum at a gas station an gave him some change. Months later I did a pizza run to beachfront home ($400-800k area) and met the same bum. He invited me in as he when to get money. All I see are piles of bags and rolls of change from the door to the kitchen and to the living room. He paid me in change.