There is some validity to this in debates, but when things start getting bad, the lefties all do seem to work together on what steps are taken. That does give me some level of optimism for change in the now, even if the future will have a divide again, I think many of us can agree that the future left-to-left divide is better than the current divide. For smaller examples, anarchists and Marxist-leninists would both be against rising fascism, and often attend similar protests. For larger examples, the anarchist and communist factions of Spain during the 1930s bonded together to fight Franco's nationalist faction. Now in all fairness, eventually the ML faction usurped the anarchists, but I'm not even gonna pretend to be smart enough to know if that's just the Soviet's influence, or communist governments in general.