I think antifascism is probably more the common thread on the left than anti-authoritarian; the distinction being that fascism is largely associated with right wing authoritarianism. The left still supports authoritarian policies. Some examples of this include gun control and censorship of hate speech.

This is not true. Left/Right and Authoritarian/Liberty are separate and overlapping spectrums. Pick your favorite post-communist-revolution country as an example of Left-authoritarianism.