This is the sort of behavior that I'm talking about, but with the term "liberals" being thrown at any leftists whose flavor of socialism you personally disagree with. Like a bunch of Christian denominations all claiming that they speak the truth and all the others are heretics and liars.

It's all too common in leftist spaces because we can't get over the minor (and not so minor) differences in our theory/philosophy to stay focused on our shared opposition of fascism long enough to act on it, while fascists naturally cooperate because it's easy to do when you don't believe in anything other than hate and whatever you're told to believe.