By accepting the Book of Mormon as a sacred text, Mormons are heretics.
And that means what exactly? A heretic is only someone who's decided to believe something other than the established theology. Pretty much every Christian alive today is a heretic relative to some other form of Christian thought. Are you a Protestant? You're a heretic. Are you a Catholic? I'm pretty sure some Catholics from earlier days would call you a heretic. Unless you can prove that you follow the exact dogma and whatnot that the direct disciples of Jesus followed, you're a heretic. And even if you do, you're still a heretic from a Jewish perspective.
Me, I'll just stick to being an infidel.