I said rotating structure/habitat, not craft (which implies propulsion).
I stand corrected. Yet my point that dismissing the engineering as merely "crossing the ts" stands.
My point stands as well:
"If, in these conditions, humans can't build a rotating habitat, then I'm sorry to say we'll never expand into space: we just don't have the brain power - by a significant margin."
We landed men on the moon and safely returned them to Earth. We know how to build manned spaceships. That does not make spaceflight a "non-problem". Look at Challenger, Columbia, and Apollo 13, if you think otherwise.
We built hugely expensive and not very safe ships that could at most get people to the moon.
We never solved the problem of spaceflight - not even close.
As for your comparison between centrifugal gravity and spaceships:
Centrifugal force creating gravity is a non-problem, not building spaceships.