In 1941, Wilson Tucker coined the term “space opera” to describe the “the hacky, grinding, stinking, outworn space-ship yarn”. Sixty-nine years later, space opera is still going strong. Not only that, it’s often seen as the defining form of science fiction. It might even be the most successful form of science fiction.
Because it is science fiction.
So you can’t have “space opera versus science fiction“. That would be like, well, like “Londoners versus Brits”. Or “Brie versus cheese”.
That’s because science fiction is not defined by its trappings. Peter F Hamilton’s Night’s Dawn trilogy is set in an interstellar federation. It is generally considered to be space opera. Ursula K Le Guin’s Hainish novels and stories are set in… an interstellar federation. They are not considered to be space opera. Iain M Banks’s Culture novels feature spaceships; Hal Clement’s Mission of Gravity features a spaceship. The former are space opera, the latter is a defining example of hard sf.
To confuse sf with its trappings is one thing. To then consider space opera a different genre entirely, though it possesses the same trappings as sf, is another. And to subsequently claim that science fiction – but not space opera – requires science, real science, is… nonsense.
Are stories featuring time travel not science fiction? What about faster-than-light travel? Aliens? Artificial Intelligence? Are stories featuring gravity, planets, stars, orbits, computers… not space opera, then?
If you’re going to write science fiction, I would respectfully suggest it helps to know what it is. Or isn’t.