Free trade is maximally effective. Maximal effectiveness usually entails moral compromises. In real life we usually take a more balanced approach towards people: you forgive your girlfriend for having a little too much in the bum, and she forgives you for not being Tyson Fury. But when it comes to big money, greed and faraway countries/abstract masses of citizens, being uncompromising and exploitative comes easier.

Any sort of regulation of slave labor/human rights/ecology in China will inevitably reduce overall efficiency and make everything more expensive. That's the only way to make things fairer, but only until some other country makes a more efficient bid and offers up its citizens as low-wage slaves.