Unlimited tolerance must lead to the disappearance of tolerance

From Karl Popper, The Open Society and Its Enemies. A continuing conundrum to which there is not easy answer.

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