The Paradox of Tolerance states that if a society is tolerant without limit, its ability to be tolerant is eventually seized or destroyed by the intolerant.
Ah that's a good point. The only think that need not be tolerated is intolerance itself. Sadly, tolerance easily can stem from the lack of backbone than from the abundance of it.
I would also propose there is a Dunning-Kruger Corollary of Tolerance, which is that the more intolerant a person is the more likely they are to perceive themselves as tolerant, and perceive people who disagree with them as intolerant.