Huh?
TNG had Michael Dorn, LeVar Burton, and Whoopi Goldberg as main cast members who were not white, three major cast members who were female at any given time, featured interracial couples (IE Obrien and Keiko), had a host of guest stars who were of all kinds of ethnicity, and had explored topics that were controversial at the time, including homosexuality. This show debuted almost 30 years ago
DS9 had Avery Brooks, Michael Dorn, Cirroc Lofton, Alex Siddig, and depicted the first African American captain, and the first female first officer as primary characters (not counting the cage), and had an even more diverse main and guest cast members, included controversial topics including sexuality, and even tackled war and the effects it has on society, as well as how governments manipulate people.....something done BEFORE 9/11, but was especially poignant and relevant in the 2000s in a post 9/11 world. This show debuted 23 years ago.
Voyager had the first female captain and chief engineer, first African american as a Vulcan, two Latino cast members (one who portrayed a Native American, though clumsily, but well intentioned), an Asian cast member, and at any given time 3 female lead cast members. It may be fair to say Voyager played it safe compared the shows before it and was not all that ground breaking, but I think it still did tackle some controversial subjects, including sexuality, and its contribution was to promote positive role models through a diverse cast, main and guest. This show debuted 22 years ago.
What these shows had in common was that they pushed the boundaries the best they could. Criticizing them because they didn't have a main LGBT cast member is not a fair thing to do, because not many other shows were doing what where these Star Trek shows were doing, and the social climate in the US, while maybe more accepting than the 1960s, was different than today. I am sure if they were allowed by the producers, executives, and sponsors, Star Trek writers would have happily written in LGBT cast members.
It really irritates me when people bash these shows and hold them to standards of today, when in reality they were groundbreaking for the time in which they were originally shot. Don't blame the shows, blame the era in which the were created.
(EDIT: another thought here: this attitude to criticize Star Trek of the 1980s and 1990s for a lack of main LGBT characters reminds me of the RETROACTIVE criticism Bill Clinton received a few years ago when Obama lifted the ban on gays in the military. People criticized Clinton for not having the "courage" to do it, and instead went with Don't ask, Don't tell. Such revisionists didn't understand how truly progressive Clinton was for doing that, and poltiically speaking, it just was not possible to completely lift the gay ban back then. I know. I was in the military back then, and know how the military was back then! Not to mention, what Obama did would not have been possible had Clinton not taken that step in the first place. Rather than blame Clinton, such critics should have been criticizing the presidents before Clinton (IE Carter, Reagan, Bush), or after (Bush II), for not doing a single thing to help LGB people serve in the military.
::Sigh:: I am sure there will be people 20 years from now who will not praise Obama for allowing gays and lesbians to serve in the military, but will criticize him for not opening it up to trans people instead.