Strange this is mentioned as the communist manifesto contains a whole chapter criticizing Utopias.
Also - establishment intellectuals from Hegel to Fukuyama to Pinker talk about how we are in Utopia now, at the end of history with capitalism and liberalism triumphant.
Marx said not only was capitalism self-destructive, with crises (like the 2008 government bank/insurance/etc. bailout), but that socialism would be self-destructive too. Hard to call someone postulating the next system will self-destruct is utopian.
Also Marx replied to socialists wanting utopian plans from him by replying he was not August Comte, and he did not want to "write recipes for the cookshops of the future".
Marx was about as unutopian as you can be, other than he thought the progress of production and technology over the millennia would continue, with effects on relations of production. Something you read on HN regularly.