(This post is inspired by the choice of a female to be the next Doctor on the TV show Dr. Who. Note that you can't say `the next Dr. Who will be female' since Dr. Who is not the name of the character. The name has not been revealed. Trivia: The first Dr. Who episode was the same day Kennedy was shot.)
I give a contrast and then say why it might not be valid:
Star Trek- The Original Series. 1966. There is a black female communications officer, a Russian officer and an Asian officer. And Science Fiction Viewers EMBRACED and APPROVED of this (for the time) diversity.
Modern Time: A black Storm Trooper in Star Wars VII (see here), a black Jimmy Olsen in Supergirl (see here), female Ghostbusters (see here), a female Doctor on Dr. Who (see here and here) , and even the diversity of ST-Discovery (see here) have upset science fiction viewers.
So what happened in 50 year?
Now I say why this contrast might not be valid. All items here are speculative, I welcome comments that disagree intelligently. Or agree intelligently. Or raise points about the issue.
1) Science Fiction fans aren't racists and anti-women, they just don't like change. Star Trek: The Original Series didn't have an original cannon to violate. Having a black Captain (ST:DSN) or a female captain (ST:VOY) was a matter of NEW characters and I don't recall any objections. (Were there objections?) If in the ST reboot they made Captain Kirk black, I suspect there would be objections which the objectors would claim are not racist. Would they be?
2) While the fans that are upset get lots of coverage, they might be the minority. I sometimes see more stuff on the web arguing against the racism then the racism itself. (A friend of mine in South Carolina told me that whenever a Confederate monument is about to be taken down the SAME 12 people show up to protest but get lots of coverage).
3) Science Fiction has gotten much more mainstream, so the notion that `science fiction viewers now do BLAH' is rather odd since its no longer a small community.
4) In 1966 there was no internet (not even in the Star Trek Universe!!) for fans and/or racists to vent their anger.
5) Some of the objections have valid counterparts: "I don't mind Jimmy Olsen being black, I mind him being so handsome, whereas in the Superman Cannon he is not." (Counter: some of the objections are repulsive:; "I don't mind Jimmy Olsen being black, I mind him being a love interest for Supergirl". Gee why is that?)
5a) Another `valid' one `storm troopers were all cloned from ONE white guy so there cannot be a black stormtrooper'. Racism hiding behind nitpicking? Actual nitpicking?
6) I give the fans back in 1966 too much credit- it was the showrunners who embraced diversity. The fans-- did they care?
6a) I give the showrunners to much credit. ALL Klingons are war-like, ALL Romulans are arrogant, ALL Vulcans are logical (except during Pon Farr), In the more recent shows like ST-TNG ALL Ferengi are greedy. So the show accepts that stereotypes can be true.
6b) Women were not portrayed that well in the star trek universe, even in the more recent shows. See 15 real terrible moments for women on Star Trek
7) Even the 1966 ST was not as diverse as I make it out to be. I doubt it would pass the Bechdel test
two other points of interest
1) In the 1960's Science Fiction was sometimes used as a way to talk about current issues since talking about them directly would not have been allowed. We can't really talk about real racism in a TV show so we'll have an alien race where they are all half-black, half-white, but differs on how which side (see here). And now? Racism, sexism, homophobia can all be talked about freely. Hence other media has moved ahead of Science Fiction for diversity.
2) Also of interest, though not science fiction: The Edward Albee estate blocks a production of Who's afraid of Virginia Woolf that was going to cast a black man as Nick (a supporting character- George is the main male character). See here. Why the block? Because that is what Albee (who is now dead) requested. What would he think now? Who knows?