...I think it is reasonable to say that opposition to homosexuality would not have been the default stance of the cultures of or derived from Europe if not for Christianity being the dominant religion in previous years. While the Communists rejected religion, they did not fully update on this rejection, but rather continued in many of the beliefs that religion had caused to be part of their culture.

Blaming lingering Christian memes for the illegality of gay marriage doesn't seem right to me, because almost all countries that currently allow it are predominantly Christian or Post-Christian. Are there any countries that allow gay marriage that don't have a longish history of Christianity?