> But those are not science fiction.
Stories based on physics and maths are not science fiction? Are you feeling OK?
> If you tell a story that is within the limits of what we know to be possible with the knowledge that we have right now, you will end up with a very boring story.
Um. Most stories in general stay within reasonable limits of what we know to be possible - are most stories very boring? You basically seem to be arguing that all stories that aren't fantasy are boring, which is clearly untrue.
> Interstellar, which makes for a nice story
Interstellar is tediously boring rubbish :P
> For example, try to write a story where the entire premise is that someone manages to construct an Alcubierre drive. You'd get ...Star Trek: First Contact.
What... no? The phase-space of all possible Alcubierre-drive fiction is not "Vulcans come to visit", any more so than the phase-space of all possible stargate fiction is "Ra gets quite angry".
There is a trade-off between speculation and realism, that leaves a very, very narrow space for an interesting story.
Part of it is due to the fact that most of modern science has been mined mercilessly for "hard" sci-fi subjects, that have now become tropes that can't form the basis for an interesting new story anymore. For example, try to write a story where the entire premise is that someone manages to construct an Alcubierre drive. You'd get ...Star Trek: First Contact. Nice movie, hey. But nothing new, there.