Strong AI could be impossible (in our universe) if we're in a simulation, and the software running us combs through things we create and sabotages every attempt we make.
Or if we're not really "strongly" intelligent ourselves. Invoke absolute denial mechanism.
Or if humans run on souls which have access to some required higher form of computation and are magically attached to unmodified children of normal human beings, and attempting to engineer something different out of our own reproduction summons the avatar of Cthulhu.
Or if there actually is no order in the universe and we're Boltzmann brains.
If Strong AI turns out to not be possible, what are our best expectations today as to why?
I'm thinking of trying myself at writing a sci-fi story, do you think exploring this idea has positive utility? I'm not sure myself: it looks like the idea that intelligence explosion is a possibility could use more public exposure, as it is.
I wanted to include a popular meme image macro here, but decided against it. I can't help it: every time I think "what if", I think of this guy.