Earlier quoted context omitted.
Known as the paradox of tolerance. https://en.wikipedia.org/wiki/Paradox_of_tolerance
If you stop treating it as a moral commandment and instead consider it a treaty which allows civilization to exist, it becomes obvious that it doesn't apply to those who won't remain bound by it. It's not a paradox. Tolerance is for all points of view that will allow the discussion to continue.
Seen in this light, tolerance is somewhere between symbiosis and mutually assured destruction, and much less wishy-washy than everyone thinks it is.