Exactly! You say you are a communist, most people in the west are shocked, as their image of a communist is some kind of nebulous villainous red army soldier, ready to appropriate their TV and their toothbrush for the revolution. So when you are just a regular person who is a communist and are willing to discuss communist ideas with someone, they are often quite willing to listen.

When you present yourself as a "Marxist" to the average person, they may not quite know what that means, and it implies that you are trying to distance yourself from being called a "communist", like you are hiding something and being shifty about your true intentions, which ultras often make worse when they gleefully quote mine some obscure Marxist thinker to "dunk" on some random person who was just trying to learn about them.

The first conversation they come away with a better understanding of communism and might find themselves agreeing with the ideas talked about, even if they were "communism is still bad though" in the moment. In the second conversation they learn nothing except that the person they were talking to is a smug asshole who thinks they are smarter than everyone else, and that has something to do with communism, so it only makes their knee-jerk reaction of "communism bad" even stronger.