“Sanism,” as it exists, is a bad term. “Clinical insanity” stopped being a real diagnosis almost a century ago and the term “sanism” gets applied to basically every mental condition, those having to do with the legal and (former) medical definitions of insanity and the much larger number that don’t.

I like “mentalism” a lot more because the more prominent pop culture meaning of the term is worthless (it’s just pop psychology) and free to be replaced, and it conveys the idea of a bigotry based on mental conditions without using antiquated language or getting into concerning implications.