First of all, Don Pope, slave labor was not "free".

Slaves had to be bought, fed, clothed, and housed

And in the north during the time of slavery, their manufacturing-based economy, which did not depend on slavery, was far healthier than the agriculturally-based economy of the south. That's one of the main reasons why the south lost the war.

If unskilled workers were paid more, then prices would be higher, but then people in the workforce would have more to spend, so the effect would kind of cancel itself out and corporations would still make a profit.

And I still don't see where unemployment is a necessary part of capitalism.