The "Tolerance Paradox" is the name used when one who values tolerance demonstrates intolerance towards someone else who is intolerant.
This phrase is often used in bad faith to show that the "tolerant left" are actually the intolerant ones when they refuse to engage with "both sides" of an argument.
Tolerance is not a moral ideal. Tolerance is social contract.
Intolerance by its nature breaks the social contract. Therefore, one who does not give Tolerance does not recieve Tolerance.
There is no paradox here.
Tolerance as social contract means that you will be entitled to live your life in peace as long as you pay the cost of allowing others to live in peace. There is nothing more to it. If you find that price to be too high, then you're no longer a beneficiary of Tolerance.
Take as an example the sentence "It is always a moral good to punch a Nazi."
I can say this while confidently considering myself within Tolerance as social contract. Intolerance is a fundamental part of Nazism. They consider the price of Tolerance too high, and so they do not pay it. Tolerance as a social contract is broken, and they can no longer claim its benefits.
Any individual is free to decide how to behave toward anyone else. Anyone may tolerate a Nazi if they so choose, but in doing so they are enabling intolerance. This causes direct harm to Tolerance and cannot be allowed for the health of the social contract generally.
Those who value Tolerance must protect it. Enabling intolerance will never protect Tolerance.