^^^No "hard" SF is plausible as true scientific speculation, which is no problem since it doesn't aim at the kind of accuracy opponents of SF pretend it does. At least, not since Jules Verne, but that was so early on he can be forgiven. Also, he was kidding himself.
Military SF is a genre where the pseudorealism is essential to willing suspension of disbelief. How does arbitrarily miislabeling the prose style help anyone shop, much less understand?
Further, how does arbitrarily labeling Kage Baker, Catherine Asaro, Justina Robson and Sandra Macdonald science fantasists make them less geeky and more cool, like Charlaine Harris, Sherrilyn Kenyon, Laurel K. Hamilton and Diana Gabaldon?
Science fantasy is a stupid term, evocative of nothing but confusion. Wells' "scientific romance" was better than that.
Calling either Wells or Verne "science fantasy" is plainly bizarre, much less someone like Olaf Stapledon. Calling Kim Stanley Robinson's Capital trilogy or Joan Slonczewski or Greg Egan fantasists is positively crazy.
There's a threadbare pretense of reasonableness, brought in by idiosyncratic notions of plausibility as the only acceptable meaning of realism. The question is why people are so aggressive about this issue? Ordinary readers have no great difficulty in distinguishing SF and fantasy. The true attempt at a bastardized blend of SF and fantasy is steampunk, which is fueled by an unseemly love of imperialism.
But for whatever reason, something is pushing buttons too hard for people to understand what they read. Or write, since claiming the difference is strictly esthetic is completely inconsistent with the claim that SF is a sub-genre of fantasy.