China's unprecedented generational explosion into the middle class happened only after Deng Xiaoping instituted market reforms. Economically, China is certainly more socialist than the west, but far more capitalist than it was in the 1970's.
So, obviously my citizenship or my country's history has no bearing on the merits of my criticism. It seems you want to have a completely different argument.
I think it's fair to criticize someone for being aware that a person is being enslaved and not doing anything meaningful about it for the same reason that it's fair to criticize onlookers who fail to call 911 on a crime in progress.
Yes, except as a full grown adult, the author never reported the situation to the authorities, took this 'secret' to the grave and even 'inherited' his slave from his parents. He said he paid her an allowance (which didn't sound like much) and also didn't make her work after she lived with them, but that's a token effort to right the injustice of decades of work without pay.