I'm going to take your question as genuine and answer in equal.
It's a bit more complicated than that. Most leftists will agree with you, the USSR and other Eastern Europe countries that were communist did a lot of damage and most likely more harm. They committed atrocities. They were authoritarian. It was disgusting.
The leftists who still prop those countries up on their shoulders are what many call tankies. Today they sing praise about Russia, China, and North Korea, but your observation is correct, they won't ever move there. These are individuals who repeat propaganda and are, ultimately, just red fascists. When you actually dig into their ideals they parallel and sometimes mirror Nazis.
I believe leftism cannot have an authoritarian element to it. I think most social hierarchies need to be destroyed. I think the only way to have a socialist society is through democratic means. Democracy in the workplace and national level. I think most of us can agree workers need higher wages and there is a wealth gap that needs to be dismantled. I think most of us believe healthcare needs to be universal, food and shelter and water, education, information (internet), speech, and much more should be free and readily available. There is this element of freedom that needs to be achieved that isn't found the countries that are "communist".
I don't want to explicitly say those communist countries wasn't "real communism", but fascists, authoritarianism, always appropriate from progressive movement. There is no freedom, especially of workers, under a dictatorship. If workers are starving, dying, being outright black bagged and killed, i don't think that can be considered communist.
I think there is a very good argument of antisemitism if you support Hamas. There is no argument for antisemitism if you support Palestinians.