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.
Anarchists need to understand that in order to make good criticisms you have to be able to address all counter-points. If we just accept them to look more objective we aren’t doing anything. So I don't see the problem with MLs defending ML states.