Make me stop, then.

I would immediately question the purpose of attempting to domineer someone's very soul to adhere to a Western secular tradition, especially when the argument most often comes up when discussing Islam and not Christianity, the actual faith that Western anglophone leftists would actually encounter that has any amount of institutional power over them. There is a strong imperialist impulse that drives this, and a lot of the criticism of Marx's more subtle antisemitism is that his tolerance of, say, Jews is predicated on ther ability to be secular and Rational™ as he saw it, even if he wasn't as dramatically and overtly hateful as Bakunin. For whatever reason the supposed incompatibility between religious or spiritual beliefs and leftist thought comes up when discussing paganism, Islam, Judaism, indigenous faiths, and so on, and least often about Christianity; rarely if ever is the expectation that one become specifically an atheist upon being enlightened questioned as possibly serving an imperialist role alongside Christianity.