Have you ever read In Search of Lost Time?
In the hero's childhood he is very often sick and bedridden, so he spends his time, mostly, reading books, typically gifts from his grandmother. These books are always chosen carefully. She makes sure to pick out ones that not only are literarily distinguished, but that have artwork by an important artist, and if possible ones where the reproduction is likewise made by a notable printmaker, etc. So, for example, if she were giving him a book of Dante, she would probably get a copy of the Inferno with illustrations by Gustave Dore. So that there is in every book that he gets and reads, an incredible layering and distillation of artistic ideas and impulses. As you can see, this places him at several removes from reality - typically his books would transform the world into art not just once but three or four times.
One of the books he has (I can't remember which) includes images of a church, in the resort town of Balbec. Whenever he brings it up with his father or his father's friends, they deride it as being an ugly undistinguished building. But he has already conceived a firm desire to go and see it, because the image has convinced him of its singular beauty.
Eventually he visits the town, and inevitably it's a terrible disappointment. The church is just standing in a drab town square, by a post office and a train station. The building is really nothing special. Over the course of the book he has many similar disappointments.
But this does not lead him to conclude that there was something "incorrect" about his initial obsession. Quite the opposite: he comes to see his ideas of these places and people (Balbec, Venice, Madame de Guermantes, etc etc) as being much more vital than their dismal, factual appearances. It's not a question of his dreams being inadequate representations of things. Rather, they are essential ideas that are evoked By things. I don't want to ruin the book for you if you haven't read it, but I will say that this way of thinking turns out not to be crazy, but incredibly fruitful.
To me this is a very good way to think about utopia. It isn't literally a plan for a future situation that could be permanent and perfect. Instead it's an impulse that one can't possibly do without.
By pointing out that this impulse can't be exactly realized, one isn't faulting it for being "unrealistic" but confirming its importance and vitality.
I also recommend Ernst Bloch's book, The Principle of Hope, as a way of thinking about this.