Lol! No one on this thread has said anything to that effect. There is actually quite a good debate going on here with both sides using Scripture.
Then it certainly is an exception. I do believe that hostility towards a belief in the Perpetual Virginity of Mary arise out of a deep hatred of it being Catholic dogma and therefore suspect. If not I suspect it would be regarded as adiaphora. Since arguments can be made for both sides using Scripture. That it is not for me confirms it is not the belief itself that is the problem but that it is a “Catholic” belief.
Just once I wish they would gripe at the Orthodox.