I think it isn't due to it being religious in general but its relation to the Holocaust specifically. We should probably also avoid fire with a Latin cross specifically because of Klan cross-burning (Greek crosses, etc. are distinctly different and don't have the same history).

but I guess I'm just a heretical commie: Opium, heroin, fent - it's all the same to me.

As an antitheist: Shut the fuck up. You clearly don't understand Marx's meaning when he said that or you wouldn't be such a sneerimg misanthrope about it.

Religion is the sigh of the oppressed, the heart of a heartless world, i.e. a coping mechanism for people who are suffering, like opium was commonly used for at the time of his writing.

I ardently hope for a world where religion is essentially destroyed and exists only in history books and old monuments, but it's incorrect and antisocial to take such a contemptuous attitude towards religion in the current day rather than see it as a symptom of the problems that actually need to be fought.

But please, don't let me interrupt you just as you were about to show us a sketch in your notebook of a hypodermic needle interposed with a crucifix or some shit like that