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 considered sci-fi to be a genre, he always argued it was a setting and that his most famous stories were detective stories in a sci-fi setting. But detective stories don't work if your world isn't grounded in something real. Otherwise the reader can't reasonably build their own theory or deduce the answer because it's based on what the author thought was cool and not what logically connects.

The appeal of something like The Expanse just falls apart if you introduce a FTL engine just because it makes for a more dramatic story moment somewhere in the plot unless there is some serious justification as to why the author didn't just break all the rules of their world (which is supposed to be our world, but in the future).

Presumably these are equally likely because you could build a DNA-printer and thereby create a dragon of some sort (not sure if it could have fully functional fire breathing though)?

You don't need to break the speed of light to get to the stars. Time dilation and space contraction mean that you can get there in as little time as you desire.

Everyone you knew on earth would be dead by the time you got back, but if it's just about you, the speed of light is no limitation at all. (The rocket equation, however, presents stupendous engineering challenges.)

I have upvoted you, and perhaps you are right that there are shades of pessimism in this perspective.

The 2020s have not been known as reasons for great optimism. The pandemic and AI culling clades of the job market have been traumatizing experiences.

I don't think it's motivated pessimism so much as a shifting tastes and changes in media. There are tons of SF stories with starships in movies, games and streaming platforms. It just happens to be the case that fantasy is more popular then SF at the moment where books are concerned.

Our astrophysicists don't even know why the universe is expanding, don't know that Lambda CDM is correct, don't know if things are universally consistent, yet we're so damned sure this is it.

We don't even know that this isn't a simulation. Not non-falsifiable, sure. But we're convinced we're bound to this solar system with our crude tools and limits of detection.

One new instrument could upset our grand understanding and models. Maybe we should wait until they get better hardware to marry ourselves to their prognostications of the end of time.

During the postwar years of plenty, people stopped dreaming. We had bold dreams before WWII, but people stopped looking at how far we'd come and started comparing themselves to everyone else. We had no mortal enemy, tremendous wealth, and "keeping up with the Joneses" became the new operating protocol.

We have more than we did in the past. The manufacturing wealth of 1940-1970 was a fluke. The trade wealth of 1980-2020 was a fluke. We were upset over an unfair advantage that won't last forever. Even today we're still better off than a hundred years ago, yet everyone focuses on how bad things are.

Maybe a return to hardship will make us dream again.

[dead]

And then there’s Cloud Cuckoo Land. (Anthony Doerr)