Marx was basically just inspired by French Revolution idea of "Liberty, Equality, Fraternity" and dismayed that it didn't work out. He came to some real insights about why capitalism doesn't achieve that vision. He changed his views over time and wrote strongly about cases where he was wrong. He didn't want anyone to idolize him in some static way or be "Marxist". He actually wasn't prescriptive, he didn't say what to do or how to structure a socialist society. He mostly diagnosed problem patterns in capitalism without proposing what the alternatives should be. Or so I've heard, none of this is my original insights or understanding.
Of people who are "Marxists" by self-description, some have been dangerous and destructive, but there are various versions and they often abhor each other. The worst of them are just as self-righteous as the worst of the Austrians.
FWIW, I think the Austrian models almost all have some truth in them. The problem is how they treat them as complete and dogmatic. They think they have it all figured out, and so they just take any situation and insist that their simplistic models are all there is to it. As a snarky critique, I think the Austrians just believe Wikipedia doesn't exist — or maybe they think it exists precisely because of the lack of government intrusion or something. They just have no insight, no model, no perspective of value on how it is that Wikipedia does exist. They are more interested in their models than in human beings (well, to be fair, I think that's similar for mainstream economists too).