One of the reasons why Trek was to powerful because it never explained its utopia and how it was accomplished. That inspired the viewers to reflect how to find real life solutions to come closer to this fictional utopia. The same way the fictional gadgets are never explained and then someone finds a way to create a flip phone in real life.
The reason why Trek got dark is not because of better drama. The reason is simple: Dark drama does not challenge anybody. It does not challenge producers, it does not challenge writers, it does not challenge actors and it does not challenge viewers. Everyone involved knows this kind of fictional drama. The product is easier to create (thus the paycheck is easier to earn) and it is easier to sell, because they viewers get more of the same, a form of fictional drama they knew since their birth.
I became a Trek fan because TNG had the balls to find a way to tell drama in an utopian environment. And thus challenged everyone involved - those who did create the show and those who consumed it. It did not explain the utopia or the technology, it left it to the viewers to find explanations and solutions in the real world. A genius concept.
Unfortunately Trek is not genius anymore. It is more of the same. Dark, gritty, about war, with villains. Boring, safe, more of the same. Thus I dont care for it anymore. Trek today is a product I dont buy, because it is simply lame and pathetic, a cynical pop culture product that challenges nobody.
I come back to Trek when it dares to challenge with Utopia again - challenges those who make it and those who watch it.