After arguing with a lefty and bringing up the fact that they were being intolerant of my intolerance I learnt about this paradox.

It's a pretty big rabbit hole of information I believe.

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

https://infogalactic.com/info/Karl_Popper

arl Popper was born in Vienna (then in Austria-Hungary) in 1902, to upper middle-class parents. All of Karl Popper's grandparents were Jewish but were not devout, and as part of the cultural assimilation process, the Popper family converted to Lutheranism before Karl was born,[16][17] and so he received Lutheran baptism.

The paradox of tolerance arises when a tolerant person holds antagonistic views towards intolerance, and hence is intolerant of it. The tolerant individual would then be by definition intolerant of intolerance.

Homophily and intolerance

The relation between homophily (a preference for interacting with those with similar traits) and intolerance is manifested when a tolerant person is faced with the dilemma of choosing between establishing a positive relationship with a tolerant individual of a dissimilar group, or establishing a positive relationship with an intolerant group member. In the first case, the intolerant in-group member disapproves the established link with an other-group individual, leading necessarily to a negative relationship with his tolerant equal; while in the second case, the negative relationship toward the other-group individual is endorsed by the intolerant in-group member and promotes a positive relationship between them.

This dilemma has been considered by Aguiar and Parravano in Tolerating the Intolerant: Homophily, Intolerance, and Segregation in Social Balanced Networks, modeling a community of individuals whose relationships are governed by a modified form of the Heider balance theory .