There's nothing inherently wrong with Marxism though (not that you said there was, I just get the impression some people are calling them socialists as if it's inherently an evil thing), they're entitled to their opinions on an alternative to capitalism, it doesn't make them bad or weird people.

I gather from what I've read here that people mostly don't get along with them because they are awful, terrible people (and honestly may not even be proper Marxists but maybe just posers, using it as a perfunctory label, idk).

I'd gladly be friends with a Marxist, but friends with an authoritarian, or a xenophobe, etc? Absolutely not. Regardless of their other political or economic opinions.

Stalin invented the term Marxist-Leninist. Before that they were just called Leninists.