This is not a Rationality Quote, but it might be about transhumanism if you squint. From a short Iron Man fanfic, Skybreak, cut for relevance:

He tells the recruits that technology will never replace them. He tells them that flight will always be there for them, that flight has to be there for them, because they are masters of the sky and what the hell were humans meant to do, except fly?

…

He knows men will never stop flying. Not because the machines will stop coming, because they won't. Not because the future's gonna step aside for him, because it won't. Rhodey knows because he's seen the future. He's seen technology, he's been friends with the biggest and best damn technologist on the goddamned planet.

And when Tony made the armour, he took away the plane, not the man. When Tony set out to fly, he put the engines literally in a man's hands, put wings on his feet, and broke the sound barrier with his fucking forehead.