For idolizing the soviet union and the people's republic of china, who have done some very evil things. Tankies always try to undermine the sins of authoritarian regimes. They keep trying to instate authoritarian regimes knowing full well that they have killed so many historically.
If you want truly based leftism, try anarchism.
Mutual aide is not really the issue with tankies, the problem is the authoritarianism. Mutual aide can be very effective when done properly. For example, anarchists tend to answer the question of "leeches" by giving them the resources to self-actualize, and if the "leech" does not care to do that, they can be kicked out of an anarchist community.