what advantages does free labor have over the "mud sill" approach to making a living?

Free labor allowed one to be independent and make their own money, it blurred the lines of classes. It didn't matter where one was born, hard work lead to a better way of life and owning property. Mudsill is akin to slavery. It exploits the poor and equates their toiling as charitable for the so called advancement of society. There is zero chance of upward mobility.