Does that mean we should never again root for radical change? Because Stalin effectively murdered millions of people? If that's what you're implying, then I would have to disagree completely.
The activism of socialists and communists that you're labelling as "utopian" involves working on community problems, fighting for local progressive legislation, practicing mutual aid, showing up in solidarity with unions, and so on. And that's how it's been for a very long time. Where is the utopianism in that? And how on earth do you look to that and see a specter of genocide?
American capitalism has plenty of genocide on its hands, from the Trail of Tears to Wounded Knee to all of the stuff that Kissinger did in multiple countries.
You realize that there are plenty of communists who don't believe in violence or authoritarianism, right?