Those people were clearly in the wrong though. After all, why join a civil liberties union if your support for said liberties is conditional on your whims?
Unwavering, unconditional support for an idea - any idea - seems like it could result in a bad time.
Personally, I'm not sure where I sit on this one, and I think there's a valuable, good-faith discussion to be had on whether free speech as we see it today, is actually a net good or not. It's an inherently complex question worthy of debate.
Pre-Brexit, there were a lot of people that really wanted sovereignty.
Post-Brexit, it turns out that sovereignty didn't make a lot of those people happy, because it got in the way of their employment or business, and it turns out you can't eat sovereignty.
Same thing happened here. It's a lot easier to defend a despicable person's right to hold a protest when they're powerless. But when people start dying that gets a lot harder to justify.
Only for those who were unprincipled in the first place. Those who approach civil liberties from a point of subjective right vs wrong are doomed to failure - the moment a case comes up that clashes with their own viewpoints, they will abandon the liberties they claimed to defend. On the other hand, those who approach civil liberties as a matter of principle face no such dilemma.
...until they remember that there are that there is more than one civil liberty, and more than one person who has civil liberties, and that sometimes one person exercising a particular civil liberty can prevent or conflict with another person exercising a different civil liberty.
Once you are dealing with a society bigger and more complicated than Gilligan's Island, you cannot escape these dilemmas.
It's kind of a fairy tale of the kind Disney sells you: if you do the right thing, everything works out for the best. We like that idea because simplicity is appealing, but the real world is complicated and conflicts with such nice notions.
In Disney movies when you do the right thing, it saves the world in the end.
In the real world when you do the right thing, sometimes all you achieve is nazis running over a crowd, and you end up with a crisis of conscience and not much to show for it.
Nothing the ACLU ever did blew up in their face. People haven't "started dying" because of the rights they defended. Instead they just got taken over by people who are immersed in your worldview and willing to parasitize and destroy any organization they can get their hands on in a belief that people should be ruled by hard-left "experts", who will make them "happy", even if they don't seem to realize it or agree.