The natural state in capitalism is that a worker owns their own means of production - their time. If one wants to trade their time into a collective, that is their time to trade. Slavery breaks this, and one of the more interesting facets of the American civil war was that the North (anti-slavery side) was much more efficient than was the South (which favored slavery), even in agriculture.
Labor is not capital (means of production), it's not being "owned", since one cannot accumulate it. That analysis is deliberately obfuscating problems with capitalism, which stem from capital accumulation. (And if anything, it is slavery that turns labor into actual capital.)
