I think I know who you mean. He’s not here anymore, but he definitely sided with the antisemites. Like a Kapo to the Nazis.There is also the Stockholm syndrome aspect to it.
People have so internalized the hatred against them that they roll over backwards trying to convince their haters that they are one of the good Jews.
I have seen it on this very site where a Jewish moderator kowtowed to a very antisemitic fellow mod.