China razed thousands of Xinjiang mosques
wsj.comHow can this be justified in the name of terrorism?
I don't single an ounce of a justification for destroying holy places.
How can I as a westerner support their (xinjiangs) plight?
Depends on how much effort you're willing to spend. You could learn Uyghurche (free textbook here: https://kuscholarworks.ku.edu/handle/1808/5624 ) visit those holy places in Xinjiang, befriend Uyghurs and learn from them in person how they'd like to be supported.
Or you can let someone else do that work instead. Maybe they'll accept donations.