Huge contradictions that can't really be worked around IMO.
E. g. MLM's and Anarchist obviously don't really get around very well.
So if you really believe in the core principles of one of the sub-branches there are quite some things that are probably not willing to compromise on...
Still I think many leftists would take any non-my-sub-idealogy leftist over libs, fash and the boguiasie.
I think this kind of internal polariaing debate in people that basically agree on the goal, just not the means, shows the dedication of leftism to doing the right thing.
Interestringy the right can always unite when it's tactically "good" as they all agree on basilly hating "others"