Huh, I've read Marx and I dont see the utopianism you're referencing.
What I do see is "classism is the biggest humanitarian crisis of our age," and "solving the class problem will improve people's lives," but no where do I see that non-class problem will cease to exist. People will still fight, get upset, struggle, just not on class terms.
Maybe you read a different set of Marx's writing. Share your reading list if possible.