An often unstated commitment to "purity" undergirds hegemony. A commitment to purity (and a rejection of impurity) is very old...a mechanism driven by evolution that has often been (intentionally or not) exploited by those in power. All religions seem to have some purity concept: how to have sex the proper way, how to eat properly, etc. Notions of purity and impurity may aid in survival. But when they get baked into social constructs, they can become rigid and evil.