My two cents on how to achieve left unity:
Anarchists: Stop using the word tankie. It pushes your fellow leftists away and pisses them off. Instead make specific criticisms of communist countries. ESPECIALLY stop calling MLs “red fash”. There is already enough misinformation going around about fascism.
Marxist-Leninists: Embrace critical support. Be willing to criticize and accept criticism of nations like China, the Soviet Union, and especially North Korea. Remember that being against US imperialism is not the only thing that makes a country good.
So many people on the left, and in this community in particular, have this ridiculous view of reality where everything is either completely good or completely bad, and the way to determine whether something is good or bad is by forming associations with other things and seeing how many of those associated things are good or bad.
There's literally no conception of the fact that people can take the same premises to different conclusions that are also reasonable, and any deviation from my exact ideas and thought process is seditious brainwashing.
When someone starts with the sincerely held principles that we ought to secure a decent living for everyone, achieve racial justice, eliminate inequality, etc, it's wrong to get mad at them for the conclusions they draw (within reason).
edit: This sounds like the tired liberal bipartisan lines (e.g. "we have to reach across the aisle and find common ground"), and that's because it is. Democrats and Republicans have the same values, those being the preservation of capitalist power structures, so they practice the dreaded "civility." Among the left, we also have the same values, so civility is a rule internally only. In interactions with non leftists, civility ought to be practiced if it advances our goals.