This article gives a clear view on Marx’s vs. Engel’s view of Utopianism vs. other utopian socialists [1]. That Marx was not opposed to utopianism per se, but rather when the ideas of the utopia did not come from the proletariat. Yet you’re right in that he was opposed to the view of the other utopian socialist, and there is tension in the views of the different socialist thinkers in that time. (I do disagree on the idea that refusing to propose an ideal negates one from in practice having a utopic vision)

That said my comment was looking mainly at the result of Marxist ideology in practice. In practice millions of lives were lost in an attempt to create an idealized world. Here is a good paper on Stalin’s utopian ideal [2].

[1] https://www.jstor.org/stable/10.7312/chro17958.7?searchText=...

[2] https://www.jstor.org/stable/3143688?seq=1