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.