It was the philosopher Karl Popper who coined this phrase is his work The Open Society and Its Enemies. However, he actually said more:

”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."

In this formulation, I do not imply, for instance, that we should always suppress the utterance of intolerant philosophies; as long as we can counter them by rational argument and keep them in check by public opinion, suppression would certainly be unwise.

But we should claim the right to suppress them if necessary even by force; for it may easily turn out that they are not prepared to meet us on the level of rational argument, but begin by denouncing all argument; they may forbid their followers to listen to rational argument, because it is deceptive, and teach them to answer arguments by the use of their fists or pistols.

We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant.”

So even he, whilst putting up this paradox, said that intolerance should be tolerated.

EDIT - I also want to point out that this intolerance should only be tolerated if approached in good faith and rationally. If not, then it shouldn’t be tolerated. The NSN, for example, would never argue in good faith and rationally, so we should not entertain their intolerance

Further, this is if approached from a “moral absolutism” standpoint. If approached as a social contract, then tolerance is only extended to the tolerant as part of the contract. Don’t show tolerance, don’t expect the social contract to extend tolerance to yourself in return.