So Star Treks I, II, III, VI and VII are all awful too, I assume, as they, in turn, threatened Earth and totally changed the Enterprise, killed Spock, destroyed the Enterprise, killed off the Klingon Empire, and killed Kirk?
None of those retconned anything, there's no issue with threatening Earth or upgrading Enterprise, and the Klingon Empire was never killed off. As for killing off Kirk and Spock and destroying Enterprise, these things are bound to happen over the course of decades. Are you being deliberately obtuse here?
You can't like a great deal of the franchise, if your standards are really this set in stone. The cinematograhpy and approach may be literally 'darker' than it used to be in TOS, the subject matter really isn't - TNG, with its happy-happy-happy approach is the exception, not the rule.
The Trek franchise stayed pretty good up until the end, with some exceptions--
First Contact being the most obvious-- but it was definitely not headed in the right direction.
The show, particularly in the first season and most subsequent 'event' episodes, has been largely about the effects of the Time War and the fact The Doctor is the last of the time lords. If you can look past that plotline, you're being very selective here about what 'dark and gritty' stuff is just fine.
It has been brought up, of course, but not in depth. The Doctor has continued to be a hero, showing his preferred child-like persona on the outside while keeping centuries of depth, and his pain, mostly hidden on the inside, and helping those in need just on general principles; they haven't turned him into a grim avenger or moronic adolescent. They have always maintained a sense of wonder, both through the Doctor's love of life and his Companions' naivete. Small problems aside,
Doctor Who is a textbook example of the right way to revive a classic franchise.
With the exception of the Borg on Voyager (but actually an exception because of the pansy-assed lighthearted way they treated the Federation's greatest threat, not any 'dark' aspects), those are some of the best things Trek has ever done. The DS9 war arc, First Contact, and the removal of that horribly childish barrier to conflict and drama in the 24th century. It brought back the spirit of the original series, that we are strong despite our weaknesses, rather than that we have none.
The DS9 War Arc was very well done, but inappropriate for Trek;
First Contact was absolutely horrible (except for the last twenty minutes or so) and the perfect example of what I'm talking about; and I have no idea what you mean by "childish barrier."
Of course he does. A storytelling style that's been popular in mainstream US culture for almost 30 years is hardly a "fad."
Of course it's a fad. I'm not talking about something that has been around since Ancient Greece or a 30-year-old storytelling style. I'm talking about pop culture tropes that have been used increasingly, and with greater extremity, since the early 80s. And it can't have much more life to it, because how much more extreme can it get than torture porn and nuBSG?
