>What motivated them? Likely he will give simpleton answers like "power corrupts" or dictatorships are evil without ever understanding the complexity of the situation.

The motivation is very simple: the Uighurs started a separatist movement, and there's little the Chinese government hates more than separatist movements. Now, many governments in the world don't like separatist movements, but you don't see the Spanish government putting Catalonians in concentration camps and forcibly sterilising them.

It's not brainwashed to believe forcibly sterilising people is unacceptable, it's basic Judeo-Christian/humanist values.