Also keep in mind that part of what makes the utopia work, canonically, is that humans have somehow evolved beyond their vices and bigotry and the fully voluntarist socialist society it portrays just works because everyone is perfectly fine working just for the betterment of humankind or personal intellectual gratification.

In other words it only works because it ignores basic human nature. Which is one reason why Star Trek's utopia isn't really tractable. The others being the technology that completely ignores the laws of physics. Free energy, warp drives and magic boxes that grant wishes.

If people want a science fiction "utopia" I'd say look at Babylon 5. It certainly has its flaws but its Utopia isn't real (because they never are,) it's an ideal that people are always struggling towards.