First of all, China didn't kill a million muslims.
Second, discrimination or racism is never right, but the arguments related to Xinjiang prisons are being used to drum up popular support for a [cold] war against China. We have a duty to speak out against our leaders, so that we can prevent tragic mistakes being made.
Second, if the USA killed a million muslims, does that make it right that China does it as well? I don't think it does.