If you want my opinion, the biggest keystone flaw in their thinking is being so ready to support/defend any nation that is or has ever described itself as communist. There is a lot of toxicity from nationalism that leads to things like pro-authoritarianism and advocating military force, and you can see it from nationalists whether they are communist or not.

Eta: But no, I don’t think this kinda stuff is inherent to communism. I think it is common in people who crave the validity of state-backed communism more than they are willing to scrutinize the history and peoples involved with the states they are supporting