Utopianism is an idea derived from the book Utopia written by Saint Thomas More. It is about an island where people are different; co-operative, not driven by greed. They do unto others as they would be done unto. People pushing the idea are trying to change human nature. They are bound to fail but it does make them vulnerable to manipulation, to becoming Lenin's Useful Idiots. Professor Congdon tells us that utopianism is like Nihilism, a world view coming from a passion for negation.
Interestingly the Wiki tells us that utopia can be translated as no-place or as good-place. Perhaps Saint Thomas More was on the right lines, viewing it as impossible.
Utopia ex Wiki
A utopia /juːˈtoʊpiə/ is a community or society possessing highly desirable or near perfect qualities. The word was coined by Sir Thomas More in Latin for his 1516 book Utopia, describing a fictional island society in the Atlantic Ocean. The term has been used to describe both intentional communities that attempt to create an ideal society, and imagined societies portrayed in fiction. It has spawned other concepts, most prominently dystopia.