Earlier quoted context omitted.
Not sure your point. It's fiction. Are we closer to finding dragons, faeries, or magic? Visiting remote planets is as unlikely as riding a dragon. But both make for great stories.
Science Fiction doesn't have to be fantasy, it can be speculative. But if your setting or plot relies on something we know to be scientifically untrue, and you don't put some effort into explaining why it somehow works in your setting, it's fantasy and not speculative. Someone like Asimov never considered his books to be fantasy and that he could just insert whatever he wanted with no justification. In fact, he never…
No, it just has to be grounded in something consistent and if the book starts by explaining the mechanics of the world(or is in a world with known mechanics), a detective story very well can work.