Arrgh. I said I would contribute, but my dream-topic seems off-topic. So here's a rambling draft of an opinion piece / personal reflection sort of thing. It fits. Trust me. And yes, the actual controversies and cultural developments in SF would take several books to truly examine.
About a dozen years ago, I attended a science fiction convention in the States and was on a three-person panel on whether science fiction had lost its cultural relevance. One of the guys, the person who, I think, came up with the topic, couldn't make it. I don't recall now why, so let's just say he lost his way. The other participant was John Scalzi, then newly-famous, and able to draw a considerable crowd. Someone recorded the session for a podcast, and there's a photo of us pretending to beat each other up, as a play on Scalzi's then-new novel, Old Man's War.
He immediately declared the panel's premise "bogus", which did not hamper lively discussion in any way. I've lost a clear memory of the progression of ideas among numerous panels since and I'm not that interested in looking up the podcast. I recall some discussion of the differing directions within SF, including adventure, scientific speculation, and social commentary. Star Wars, Scalzi noted, gave pop-SF a fresh start. SF films from the 1970s-- Logan's Run, Soylent Green, and such-- tended towards overt social commentary. In the manner of The Prisoner and Planet of the Apes, they served up weird, satiric takes on our world and generally ended with a twist. The 1977 film that would later be retitled Episode Four: A New Hope made the genre look fun. Hey, look! Laser switchblade! Of course, in the context of a morally murky and rule-changing era, the culture's embrace of a thrill ride with obvious Good Guys and Bad Guys, Hat Culture aliens on the periphery, and, uh, groundbreaking roles for women could be construed as social commentary and, therefore, social relevance.
Flash forward to the present. The genre has had its share of controversies. The factions are many, but a simplistic, New Hope sort of breakdown might look at people who prefer an imagined retrofuturist Good Old Days of male heroes v. social justice-learning writers who politicize everything. The Hugo Awards have made an effort to be more inclusive. In the past, the major awards went almost exclusively to White American and British Men. That isn't the case anymore, and some fans have decided that amounts to discrimination. The past didn't discriminate, those fans argue. It was just white men who happened to be doing all the writing, and if (fill in the blank) wrote books that were as good, why, of course they should win the awards. But let's not make it an Issue.
It would be wrong to characterize all of these people as SF rednecks and sick puppies. Many of them were readers of works that expressed socially progressive messages, from a certain time and place. Anti-racist allegory on classic Star Trek? Sure! Contemporary works treating gender as something other than a simple binary? Sheesh! Do we really need to be so dang political?
John Scalzi, without necessarily trying, became a target of their ire.
Think about it. His best-selling first novel clearly showed the influence of Robert Heinlein, a man idolized by certain fans in particular. Scalzi's politics were not Heinlein's, but he did identify himself as a moderate conservative. A certain wing of SF fandom saw him, initially, as their guy.
That honeymoon ended quickly. He was moderately conservative by the standards of pretty much everywhere in the developed world except the United States. In fact, he spoke and wrote on behalf of progressive causes. He penned an excellent essay on why being born a white non-queer male was the equivalent of the easiest setting of a videogame. It didn't mean you would be guaranteed a win, but the inherent privilege gave you an edge, one you might not notice you had. A popular convention guest, he decided he would not accept invitations from conventions that did not have policies regarding harrassment, accessibility, and a commitment to diversity. He joined in the condemnation of people who promoted the odious notion of Fake Geek Girls. And yeah, when the topic arose, he was not silent on some of the past, problematic aspects of fandom that were being dragged into the light.
As much of fandom embraced Scalzi, certain other fans felt betrayed by him or, rather, the person they wanted him to be. Scalzi, to his credit, responded by being the person he actually is, and fuck them.
All of which to say is that some literature and media may be more overtly political than some other literature and media, and, sure, some writers and creators damage their works by being awkwardly political, shoehorning in contemporary issues where they do not fit. That kind of relevance cannot be decorative; it must be earned.
But it's all socially relevant.
SF (or whatever genre) hasn't lost its social relevance, but it may not always be where we left it.