After reading a significant number of books from the early 19th century, I noticed that a lot of the better known authors were "communist sympathizers". Which prompted me to examine what communism must have looked like back then, before the full horror of Stalin, and the excesses of the Cultural Revolution. My conclusion is that it must have looked pretty good.

But then we all know how the story turned out, and however good it looked back then, that was an illusion. And if you had banned criticism based on how bad it looked you would have missed out on the chance to avoid some communism's excesses and failures.