Over at The Orthosphere, Richard Cocks has a post addressing this phenomenon. At one point in his post he writes:
As I’ve mentioned elsewhere, most of my students think that the greater horror they can “tolerate” the better people they are...
This reminded me of Lawrence Auster's First Law of Majority-Minority Relations in a Liberal Society. This Law (he was writing about a decade ago) he defined as follows:
The more troublesome, unassimilable, or dangerous a designated minority or non-Western group actually is, the more favorably it is treated. This undeserved favorable treatment of a troublesome or misbehaving group can take numerous forms, including celebrating the group, giving the group greater rights and privileges, covering up the group’s crimes and dysfunctions, attacking the group’s critics as racists, and blaming the group’s bad behavior on white racism.
It's possible that what Richard Cocks observed amongst his students goes some way to explaining Auster's Law. If you believe that the worse the behaviour you can tolerate the better a person you are, then the more dangerously a minority group behaves the more you will deflect blame from the group, preferring to target the majority instead. This is what homosexual liberals did after Orlando: they proved their commitment to tolerance (meaning a willingness to tolerate the "other") by stridently attacking the mainstream.
Why would a liberal society develop along these lines? It flows logically from liberal first principles.
If you think there is nothing of inherent worth external to the individual, then what matters is the act of autonomous will in self-determining one's own subjective, self-created values. The important thing is the freedom to self-determine (the choices themselves don't really matter, rather it is the unencumbered act of choosing that brings value).
But if this is a value for me then it must be so for others too. So there must be a system within which I get to have my autonomous choice respected, whilst at the same time I respect the choices of others. This then generates a liberal morality, despite the liberal starting point of believing that there is nothing of objective value existing as part of the nature of things.
The liberal morality is based on the idea of non-interference in autonomous choice making, and this makes qualities such as respect, openness, non-discrimination, non-judgementalism and tolerance key moral terms in a liberal society. Therefore, the more tolerant you are, by the standards of a liberal morality, the better a person you are.
Of course, if you are thought to violate the principles of tolerance, then you won't be tolerated but instead attacked for bigotry, discrimination, racism, sexism, homophobia and so on. And it is easy to violate the principles of liberal tolerance, because once you assert that there is any objective truth for people to be guided by, or non-liberal institutions or traditions for people to love and identify with, then you are violating liberal first principles (particularly if you assert any of these as public, rather than as merely private, goods.)
I know this gets complex in the end. Liberals end up supporting a less tolerant religion rather than a more tolerant one in the name of tolerance. But there is a kind of logic to it, if you accept the liberal starting point. If being tolerant is what makes you a good person morally, then you demonstrate this by being willing to tolerate in your society the most challenging "other" group and explaining their wrongdoing on the faults of your own society or tradition.