The argument is not "Marx therefore bad," it's that this is a useless observation. You've selected axioms that necessitate your conclusion. It's like me saying "the most moral thing anyone can do is preventing a human death, and therefore everyone here is immoral because they're writing comments on a message board instead of flying to an impoverished country to feed a starving child."

That's true, given the predicate. I don't know why it would be relevant, since -- just like with your comment -- nobody has conceded this definition of morality. The conver preceding is not obviously rooted in Marxist class struggle, so I'm not sure why you're framing it thus (whether you use the words or not.)

Your argument depends on everyone agreeing that, unless a person's basic need for house and food are totally met first, anything they do in pursuit of those needs is compelled and not voluntary. This is not an agreed upon predicate.