I feel like this is part of the myth, and maybe you're buying into it a little bit too much... that TNG was this light and fluffy romp while DS9 was a bastion of darkness and complexity. I can cite just as many conflicted characters from TNG as I can from DS9. I can cite just as many dark themes and commentaries on the failings of human nature in TNG as I can in DS9. I can cite just as many silly comedic endeavours in TNG as I can in DS9.
Boy, I would love to bet on that. By all means please list all those more complex TNG characters because I'm sure quite a few of us can have fun with that. When TNG was going off the air and Paramount was putting out those TV specials to celebrate its run I recalled one in which Berman was discussing the change and growth of the TNG characters over the course of seven seasons. A few examples of this "growth" were Riker growing a beard, Troi getting a costume and hair change and Geordi becoming the ship's engineer! Laughable. That ain't growth. The complexity and so-called growth of TNG's characters were superficial at best. And at best a TNG character mave have gone from A to B or perhaps A to C. DS9 had characters that went from A to M or maybe even further. Heck, D9 had recurring characters that displayed more growth and complexity than the main TNG characters did over a span of seven seasons. And don't get me started on where Sisko, Kira and Bashir started off and how they ended up by the final episode of DS9 (as compared to the seven year arc of Picard, Data and Riker).
As for dark themes you had people like Kira the terrorist who made TNG Worf look like a mild saint. Is there anything in TNG that matches Sisko's decisions to use a chemical weapon to posion a planet, be complicit in a murder and a coverup just as long as he could trick a galactic empire to join his side in a war or basically suggest to his commanding officers to do whatever it takes (::cough:: kill ::cough:
the leader of an ally empire who was getting in the way? Did TNG tackle terrorism like DS9 did, did it touch upon the religious zealotry like DS9 did, did it show us any of the ugly underbelly of humanity (and Starfleet itself) that DS9 did from time to time? Did TNG ever present a universe in which idealism couldn't work in the end, other than confrontations with the Borg of course? I'm just scratching the surface here and could go on for a long time but I just realized I don't want to be typing this all night.
Granted DS9 wasn't as dark as, say BSG or perhaps even SGU. That is overblown to some extent. But it was a hell of a lot darker than the other Trek shows. It wasn't every Trek's fan cup of tea and I don't begrudge anyone for feeling that way. But let's get real. TNG and DS9 are two totally different shows.