Trouble is, it's come to imply difficulty, something arid and arduous, something crabbed and restricted, and of limited appeal to anyone who isn't a stone science junkie who knows her muon from her pion, the difference between RNA and DNA coding, and the meaning of every acronym NASA has ever coined. Not that there's anything wrong with that, but there can be too much emphasis on the science and not enough on the fiction, on the weight of cold fact rather than flights of imagination. Too often, so-called hard science fiction strives to be dully convincing, and forgets to be amazing.
And in any case, the definition is mostly redundant. Any fiction about the world as it is, rather than the world we imagine it might be, sticks to the facts. Isn't much of the enterprise of modernist fiction about realism - about the accurate replication not only of the external world, but also of the inner world, the world of the mind? And aren't we living in a world that's driven by science and technology? Isn't the present too often framed as being 'just like science fiction'? Which is to say, just like science fiction in the movies, which is rooted in science fiction from the 1950s.
The world as we know it is one thing; science fiction should be about something more. Should use the known as a jump ramp into implied spaces and possibilities. Should respond to the weirdness of actual science rather than reusing received notions and used genre furniture. Should be irresponsible. Should stop arguing with itself. Should fly.