Marx was just a philosopher. The crimes of communism were perpetrated by the its implementers.

I'm replying because we should not attack the philosophers, regardless if we agree or disagree with the theory. I personally disagree with Marx's theories, for example the Labor Theory of Value, it is dashed by advances in technology like AI. He is 'wrong' in the 21st century, and we have the technology.

But without theory, at least, we cannot possibly imagine the best implementation, or learn any lessons about what to or not do.

Writing a book cannot possibly the worst thing ever. But ideologically interpreting that book, in a way that leads to worse outcomes for the people, could be.

It applies to any book, especially "holy" ones.