Paradox of intolerance

Philosopher Karl Popper defined the paradox of intolerance in 1945 in The Open Society and Its Enemies Vol. 1.

Less well known is the paradox of tolerance: Unlimited tolerance must lead to the disappearance of tolerance. If we extend unlimited tolerance even to those who are intolerant, if we are not prepared to defend a tolerant society against the onslaught of the intolerant, then the tolerant will be destroyed, and tolerance with them.