It is not wrong for individuals to choose to assimilate. The deliberate and systematic destruction of other cultures - which China is engaged in on multiple fronts - is wrong.
The fact that a country or civilization has past sins should not be a disqualification from taking a moral stand in the present. Some form of mild hypocrisy is vastly preferable to sitting silent while a country destroys another culture or puts it's Muslim population in concentration camps.
Suppose someone's great grandfather stole from my great grandfather something I was supposed to inherit. They inherited it instead.
It remains stolen property that belongs to me.
If someone dies and they owe money, the creditors have a claim to the estate.
If their claims exceed the value of the estate, they are out of luck; they can't go after other parties to recover everything.
If someone dies and leaves your their house, but it is mortgaged, then the mortgage likely has to be paid off before the title is transferred.
Creditors having a right to the estate means that you can't borrow (or steal) something, die, and have that property pass it to a heir free and clear.
Hypocrisy is rarely a substantive counterargument. It's much more often whataboutism.
Human rights are themselves a fairly recent idea. I can't think of a single powerful country/empire that hasn't committed them to some degree. And things were much worse in the past.
History is prologue, not destiny.
Source: Am South Asian.