Do religious demagogues have any rights to denounce someone as a heretic?

The demagogues have every right to claim that someone is a heretic, and sensible people have every right to respond that they are full of it. Nobody has exclusive rights to decree what is debatable, and that is a very good thing indeed. A particular religious group has the right to prescribe what its adherents should believe, and people who don't like that have every right not to adhere.