The Sanist Corollary to Godwin's Law
Basically this: Within an argument, the first person to use hyperbolic claims of mental illness to discredit his opponent(s) has lost.
The Sanist Corollary is not a form of censorship, although it might be a way to recognize that a discussion has reached its rational limit. That realization could terminate a conversation.
It is merely a flag for a broad family of hyperbolic appeals based in one way or another on name calling that refers to the supposed mental un-wellness of an opponent or others holding opposing positions.
Sanism, aka mentalism, is an authentic term used for roughly 50 years, that relates to discrimination of the mentally ill.
Sanism like other well known isms --racism and sexism--is about sweeping, stereotypical prejudice that fosters a climate that facilitates discrimination.