Nerd around long enough, and you'll hear somebody point out that there are no gay characters in Star Trek. It's true, and it actually goes beyond omission: on at least one occasion, a character strongly implies that human same-sex relationships are completely unknown, and winsomely suggests that maybe, someday, the human capacity to love won't be so limited. The only unstraight characters ever shown are in the Mirror Universe, where evidently all women are bisexual.
Of course, Star Trek is a television show, and is subject to the limitations of television shows. When Gene Roddenberry was producing a colorful space western to fill the Friday night time slot after T.H.E. Cat, he could be forgiven for not plotting all the socioeconomic implications of his utopian society. When a script made reference to the fact that the Federation had abolished money, I doubt there was a debate in the writers' room over economic incentives and state compulsion. And for most of the show's run, gaiety was a fairly contentious subject that a TV show could be forgiven for avoiding. But as nerds like me take the show's universe at face value and start spending way too much time deconstructing it, the undercurrent of the stories starts getting pretty sinister.
First off, again, there's no money. This is superficially reasonable: they have replicators, which can make anything you want, so why would you need to buy anything? But people also provide services, for which they're obviously not paid. This may make sense for personally rewarding jobs like archaeologist or engineer, but how many people, honestly, feel such a personal calling to clear dishes in Ten Forward that they'll ship out on a years-long assignment to do it eight hours a day unpaid? Later writers addressed this by creating latinum, a medium of exchange that can't be replicated and which serves as currency for a thriving galactic market economy, but the Federation uses it only when dealing with "alien" societies. Her own citizens do scut work for nothing. When interacting with 20th century humans, Captain Picard tells them dismissively that humanity has "grown out" of the "infancy" self interest.
Humans in the federation are, again, also uniformly straight and monogamous, expressing shock at "nontraditional" relationships that were out of the closet three hundred years earlier.
Perry de Havilland sums it up succinctly:
How many gay characters crop up in Star Trek's Federation? How many non-conformist extroverts? Any sign of a counter-culture? How often is an internal voice of political dissent heard in the Federation? The only dissidents shown, the Maquis, were forced into armed conflict with the Federation when it betrays them to the fascist Cardassians. The only attempts at political change shown were a couple failed attempts at a coup d'état by elements of the Federation's own military, neither of which had liberty as their objectives. The Star Trek Federation is a dystopian nightmare: smiley face totalitarianism with a California "liberal" vibe...
In short, Star trek presents a future in which the great majority of humans simply don't act like humans, and seem very happy to be forced into specific roles by an omnipresent semimilitary government with the power to move people around involuntarily at will and to incapacitate people en masse without injuring them. It can also instantly identify and locate an individual person anywhere on a planet, and has an essentially infinite capacity to store and coallate all records. It has personnel who can literally read minds, and employs them as ships' counselors. The establishment's ability to identify and neutralize resistance is effectively absolute.
And all this follows the defining divergent event of Star Trek's fictional timeline, the Eugenics Wars, a world-shattering conflict caused by ambitious and disastrous tinkering with the human genome.
When you put way too much though into TV sci-fi, it's impossible to escape the conclusion that Star Trek's humans have been artificially homogenized, genetically engineered to eliminate variation and dissent. And this unanimity has been enforced for centuries by a singular government with the ability and willingness to forcibly suppress any new variation from the established order. It's not quite a boot stomping on a human face, but it sure as hell undermines the utopian feeling you're supposed to get from all those clean hallways and pocketless jumpsuits.