how could utopia not be a desirable goal? Utopia is, by definition, desirable. (Of course, different people have different utopias.) It is unobtainable, however, as you note.
"Utopia" is a word coined by Thomas More, combining "eutopia" (good place) and "outopia" (no place). For example, the Walrasian general equilibrium system (as codified by Arrow & Debreu) is a utopia (from the NC economics perspective). It's similar to Edward Bellamy's non-market utopia in terms of being both ideal and unreal.
JD