Charlie Jane Anders' exploration of the turning point in the eighties when science fiction movies took the leap and became franchises, rather than one-offs, is a wise look at the commercial developments that shaped the entertainment landscape we live in now. But as much as inevitable sequels to sci-fi movies generally trouble us these days, the move towards franchising also represents a truer understanding of the possibilities of science fiction.
Star Wars couldn't have ended with A New Hope because the story wasn't over: the Emperor was still in power, and the conflict between the Empire and the Rebellion hadn't reached a crisis point. From a more traditional sense, it wasn't clear yet whether the narrative was a comedy or a tragedy, if it was going to end in what seemed like any of several possible romances, or in definitive defeat. But Star Wars didn't have to end, and Star Trek didn't either, because there were still possibilities left in their universes to explore.
The defining characteristic of science fiction isn't any one character, any one conflict, any one plot. It's that the story is set somewhere else, where the rules of that universe are not the same as our own in ways that are governed by advancements, or different possibilities, in science. Given that, it's equally valid to do a one-off story or a meandering, generation-spanning narrative. Good people working within the genre should know what they're doing, and what its—and their—limitations are. If your motivations for continuing a story are driven by profit rather than the needs of the particular story, you'll make bad stories. If you make a lot of money off a story that demands three movies, or a movie and a novel series, or a series of cartoons and a lot of comics, there's nothing wrong with doing good for your wallet and the world of story.