Man gives indifferent names to one and the same thing from the difference of their own passions; as they that approve a private opinion call it opinion; but they that mislike it, heresy: and yet heresy signifies no more than private opinion.
--Thomas Hobbes, Leviathan
I think there's more to it than that. To label an opinion heresy is to claim that it deviates from the majority opinion, whether or not that is actually the case.
Sort of related: The Bolsheviks were clever to call themselves Bolsheviks; the Mensheviks probably outnumbered them at the time of the split, but failed to contest the nomenclature.
Here's the new thread for posting quotes, with the usual rules: