Essentially the same thing? Would you rather your mother were called a "heretic" or a "whore"? If it takes more than a few seconds to figure it out, don't bother responding.
Gosh, is it OK if I respond? Gee, I hope so.
Maybe you're just sensitive to the word "whore," but I see no real difference between "heretic" and "whore" in this context. In fact, I think "heretic" may be worse. Calling someone's religion a heresy is extremely harsh, don't you think?