But they said "has yet to content with"

Unless you do in fact mean that every single system of governance, including things before slavery that are hard to conceptualize under one framework, extreme state control (whether you believe NK, USSR are actually socialist or not), etc. etc.

I'm not making a pro-capitalist argument, merely the point that

And ignoring the issue of slavery historically-- "has yet to content with"-- does seem a bit of a deliberate sidestep. Of course capitalism will be the primary consumer of slave labour, but slavery, absolute poverty, etc are lower and falling. Further, modern slavery is completely terrible but less severe than chattel slavery, or slavery that came before that.

But again, my argument was never that capitalism is better than anything else, merely that it isn't the most evil thing. Genocide might be. Or something completely different.