The one case in which I allowed that it might be reasonable is if an impoverished and disabled person paid what little he could to someone who would otherwise have nothing. That is just the pooor helping each other out. If I am able-bodied and could do it myself, certainly, I owe him at least minimum wage.
You acknowledge that the worker and invalid both come out ahead in this example.
My question remains: Since you recognize the alternative to the worker is nothing, how is he worse off based on the relative wealth of his employer?