To add to this, to be a Marxist is to be non-utopian. And many arguments against Socialism/communism are arguing against utopianism. To be Marxist is to be a Scientific Socialist. Or in other words: you believe that society, the economy, etc, should be for the benefit of as many as possible, including through the democratic control by those who the economy serves. As well, this implies a need to criticize past decisions (socialist or otherwise), including your own decisions, and develop a better working view of the world.

So anyone who blindly says the USSR or China is amazing, without consideration for the problems associated with the way decisions were made, the decisions that were made, or anything like that, aren't being good socialists.

I might call them the reactionary left.

And to bring up critical consumption of media: there is a lot of misrepresented information about every non-capitalist state, and every non-american ally, for clear geopolitical purposes. While awful things certainly did happen in the USSR (for example), amazing things happened as well. When comparing the "bad" and "good" with the western (imperial core) countries, a more honest assessment can be made. Ultimately helping us all envision how a better world might look.

And that's dangerous for established power structures.