I question the occasional use of the word utopia, to describe Star Trek.
I don't think Star Trek is utopian. Progressive maybe? A work of enlightenment rationalism? Or revolutionary in the historical sense? These are all very different concepts from a utopia. Perhaps the idea that fans are advocating a utopia should better be framed in different language (as they are not really doing so)? A progressive vision of hope, vs. a normalised vision of today, perhaps? I'm not sure any of Star Trek is utopian in the formal sense of the word. The Federation fights wars, has vestigial social problems, and the show was always made with flawed characters, who could not always embody wisdom - the original writer's guide calls for a story about real humans.
Perhaps the real issue being discussed here is the value of using science fiction to set a better example, vs. using science fiction to show today's paradigm lasting forever. Star Trek imagines a better example of humanity, but retaining all the usual pains of living, and it explored dystopia through the planets they encountered, plus their occasional brushes with the unwise and the insane - each being a philosophical thought experiment.
I think exploring how 'Thing Can Be Better' is actually a powerful tool for a social reformer. The act of imagining the wrongs of today being righted, can itself be an inspirational act. Who, in the 1800s, could imagine a world without absolute monarchy, except those who had read about Republics and knew they were theoretically possible? Empiricism merely tells us what is, but reason allows us to imagine what could be. The normalisation of a piece of progress that people hadn't dared hope for can be an extraordinary thing for people to see. Dr King realised this when telling Nichols to stay on the cast.
One of my concerns is that in normalizing the problems of today, into the far future, Star Trek may be unwittingly turning into a cynical conservative force. I don't mind cynical science fiction - I can accept a variety of perspectives in different works - but Star Trek dared to imagine a society where racism, unemployment and poverty were consigned to the dustbin of history, for example. While people have argued for a Basic Minimum Income for centuries, and pilot studies have been conducted, ask a member of the established order and they will be dismissive that change will ever happen - like every other expansion of rights before; the vote, ethnic equality, gender equality, LGBT equality, etc, the issue might just be one of imagination, and we will never know without trying. Star Trek once imagined the continued expansion of our rights as a matter of fact; but now it imagines active interference in foreign affairs, the assassination of alien Heads of State, suicide bombers, the contemplation of genocide.
At the moment there is a resurgence in literature extolling the virtues of the enlightenment and scientific method, arguing it has incontrovertibly proven itself as a tool of human progress. For a while it became fashionable to cast doubt on these forces. Star Trek resolutely imagined their natural extension into the future in eras where that was not fashionable. By almost all measures of progress, humanity is improving - in fact, the danger right now might be that while this is happening, people are more sceptical than ever, due to a media that presents only the bad side of current affairs. Will Star Trek be one such media?
I don't think Star Trek should ever aim to present a utopia, but then that was never the argument of DSC's critics anyway, the debate was just framed for them in those terms.
Think of this as one more literary technique in the arsenal of a writer.
