How was Kirk having to kill his best friend that became a literal destructive God and was getting stronger every day a example of TOS being not a utopian future? Kirk was trying to not kill him most of the episode and only did it because Gary had become a danger to possibly the entire galaxy.
I was talking about the angst, as in the previous complaint about "angst-driven" characters.
The "utopia" thing is arguably a different issue, although I can argue that TOS was never as "utopian" as some modern fans like to claim it was. And even TNG conceded that its "utopian" ideals were sometimes more fragile than they wanted to think they were. Remember "The Drumhead"?
Ideals, almost by definition, are something you aspire to but too often fall short of. That's what make them ideals.