But criticizing Muslim antisemitism is anti-left, and there's not much point in criticizing racism if you don't have the left wing onboard. So Foxman is doing the right thing.

My tongue is only partly in cheek here. By criticizing particular instances of antisemitism, a larger message is sent which speaks to those not explicitly engaged with. That's worth something. Given the possible harm that could arise from criticizing Muslim antisemitism -- basically, a shitstorm -- it's worth more than the alternative.