One deranged man not liberals in general. There have been numerous right wingers shooting up churches and mosques and planned parenthood buildings.
I'd say it's the people going "But not MY side!" that we really need to be worrying about here.
But it is hard not to see that extreme ideology drives the agenda of one or a few sides, while most sides are willing to compromise with reasonable, evidence-based solutions that the ideologists reject outright. It is irresponsible to say in that case that both sides are being unreasonable - that false equivalence promotes an unhealthy stalemate and gives cover to those who blindly delay progress.
Liberalism in today’s society is stuff like taxing people to pay for health care, or living wages, or supporting the right of workers to unionize.
The Weathermen’s stated political goal was to overthrow U.S. imperialism. That is not something I would lump in the same basket as liberalism.
So I would say that this isn’t an example of liberal thinking at all, whether from the 60s or any other decade. Just because it isn’t “conservative” doesn’t make it liberal, and trying to lump everyone into a false dichotomy is rather Fox News, in my opinion.
But maybe that was AIM, not Weather Underground.