I’m not even sure it’s fair to call it a stereotype. There is a verifiable trend of homophobes in power that are gay or bi. Particularly in politics and religion. For garden variety homophobes, sure. It’s a stereotype. But the ones that are actually influencing others and pushing policy, there’s far too many of them that have been caught with their pants down to simply dismiss the trend as one. Is it harmful and unproductive? Yeah. Is it incorrect? More likely than not, no

This seems like a testable hypothesis.