Language versus reality
I know that every single nation in history that has thoroughly adopted communism as its means of organizing its society has become a totalitarian, poverty-stricken hellhole.
Regardless of what theoretical communism is supposed to be like in the dreams of insular academia, those of us living in the real world picked up the clue a long time ago, and have a tendency to be suspicious of anyone selling Marxism as an ideal way to run things.