Liberals do tolerate, and have tolerated, the dissent of people who have disagreed with liberalism. (By "liberalism" I mean Enlightenment philosophies, not "the left wing of the U.S.".) (In this post, I'm speaking in generalities and making some assumptions...)

The problem is that a subset of the people that were so tolerated (let's call them Visigoths) have now taken control of the academies and other institutions (to varying but increasing degrees), and are establishing their own new principles—which are incompatible with the liberal principles, so they're getting rid of the latter, and also pushing out the liberals themselves. The Visigoths do not tolerate dissent, so while the Visigoths were allowed to thrive in liberal academia, liberals are not allowed to thrive in Visigoth academia.

The Visigoths didn't get there by reasoned argument, nor by democratic majority. It seems to have been a combination of (1) mendacious argumentative tactics (e.g. dismissing one's opponent as "privileged" or even as an oppressor, essentially an ad hominem; falsely smearing one's opponents as "racist" [if pressed, they claim to have redefined "racism"] and similar terms; using guilt by association and other tactics to smear one's opponents as Nazis or other villains; responding to objections by saying "Look at these horribly oppressed victims; your concerns are invalid" [optional followup: "the fact that you have the luxury of caring about that concern shows your privilege"]); (2) shaming, intimidation, and bullying tactics (some of which are closely related to the smearing); (3) claiming to represent genuinely good causes that came before them (i.e. those for equal rights and equality before the law), and using that to win the support of the naively well-intentioned and to malign opponents as being opposed to the genuinely good stuff; (4) using university classes for recruitment and training, in which some of them (as professors) teach their views while suppressing dissent (finding various excuses for doing this in a nominally liberal institution); (5) despite being a minority, aiming to sound like a majority by being loud and suppressing dissent via bullying and mob targeting.

It's a pretty interesting accomplishment. Some of it was consciously arranged; much of it is probably not, and is out of control of those who laid the groundwork. The animating mindset seems to involve always looking for oppressor-victim dynamics: always looking for someone to hate, and someone in whose name to hate. The ideology is inconsistent enough to almost always give a way to find words to condemn one's chosen target (one example: roughly speaking, a work of media can be condemned as "exclusionary" if it doesn't have certain minorities, as "tokenism" if it has them but portrays them the same as everyone else, and as "stereotyping" or "cultural appropriation" if it has them and tries to portray anything specific to that minority); probably as a result, different branches of the Visigoths fight each other a lot, which may partly explain how they get good at fighting. I suspect the sense of how to choose targets is dictated primarily by primate-dominance-contest social instincts, which likely work pretty well or else there would be a lot more chaos than there is.

Is there hope? Ideally, we could get an "everyone knows that everyone knows" moment where the well-meaning majority recognize that the Visigoths are fundamentally just destroying things and not seriously helping those whom they claim to protect (e.g. policy recommendations like affirmative action and mandatory sensitivity training are counterproductive; telling people not to aspire to "colorblindness", because it demonstrates privilege and probably racism, is counterproductive). But I doubt that shooting down particular proposals is going to work, nor would firing everyone who seems like a Visigoth be good or feasible. One interesting proposal is to get the Visigoth ideology classified as a religion, and therefore forbidden to be taught uncritically in public schools. That would be appropriate, but on a few levels I'm not sure if it's feasible. Perhaps because I'm in an immunizing mood, I wonder if it would work to get people to recognize the underlying Visigoth mindset—the "always searching for someone to hate, and someone in whose name to hate", the acceptance of logical inconsistency and ad hominem and redirection and everything else—so that, when exposed to Visigoth teachings, their reaction is to attack the logical weaknesses and eventually to perceive the destructive mindset that generates them.