The fight against racism is perpetual, fine. There are two camps in that fight, the racists and non-racists. The non-racists have decided to apply the unique strategy of removing people from their camp and adding them to the opposite camp: every time a non-racist says something not correct enough or God forbid even wrong (e.g. on twitter), they are ejected into the other camp. Eventually the other camp's grown from a fringe phenomenon to being noticeably large and everyone laments. In this perpetual fight, the non-racists and non-fascists have chosen a losing plan of action. Maybe they should reconsider instead of digging in their heels.
"It wasn't very long ago that the US used state power to physically ostracize and divide its citizens by race and religion. That, for whatever reason, isn't considered an act of self-weakening, but (occasionally misdirected) observations on social media about the former are. That, to me, is telling. "
I don't know why you think that it wasn't, but obviously it was a huge act of self-weakening and that besides the moral dimension is probably an important reason behind its rectification.