Setting aside the question of whether this has actually happened like you say it has, the much broader critique I'd offer is that nobody who was defending free speech from the left in the 1970s [0] would be surprised that hate groups are allowed to operate under the cover of those protections. It used to be taken as a given on the left that free speech is so important that it is worth defending the right to the worst kinds of speech.
I see this a lot, recently -- this sentiment that yeah free speech is important, but you have to consider that nobody expected it to be used like this -- and that's wrong. Your liberal predecessors did know that it would be used like this and they explicitly and clear-headedly defended it, anyway.
[0] The ACLU defended literal Nazis: https://en.wikipedia.org/wiki/National_Socialist_Party_of_Am...