TIL about the Cagots, a group of people in France and Spain who experienced systemic hatred and discrimination because... they were Cagots.
They weren't any different from the other people living near them - same skin and hair color, same language, same religion, etc. - but if you were born to a Cagot family, you were a Cagot, and the rest of the people hated and shunned you. And nobody nowadays knows why; the origins of the discrimination have been lost to time.
https://en.wikipedia.org/wiki/Cagot
@woozle @noelle I don’t think it needs to be a threat, even. One of the explanations for the stability of cultures with minimal social mobility (caste systems, strong class systems) is that they forestall resource-use that would otherwise go into competition and can therefore keep more people alive. (So attempts to change kill a lot of people during the transient chaos and change gets a justly bad reputation.)