That's a myth, Star Trek was never particularly progressive.Star Trek has always been pretty progressive ...
They only had minorities on the bridge because NBC demanded it but Roddenberry had only white men as part of the main cast (he could have had a female first officer, NBC liked the idea the just didn't like Majel Barrett and Roddenberry refused to recast and lied instead than NBC nixed the character).
While Star Trek was on the air other shows had female and minority leads, I Spy (Bill Cosby), The Avengers (Diana Rigg) and Mission Impossible (Barbara Bain and Greg Morris) for example.
I really like Star Trek but it was never progressive, it's 2016 and in 50 years they haven't even managed to include LGBT characters, something Cheers did in 1983! It was only one episode but a sitcom in the early 80s did it and the oh so "progressive" Star Trek didn't although the bulk of its episodes aired in the 90s and early 2000s.