It's completely reasonable to think that no one can fly. But then we nibble at that, cuz we want to fly; and we add caveats to the rule. it becomes "People can't fly:"
- without mechanical assistance,
- without at least a wingsuit and a tall place to jump from,
- in standard gravity,
etc. So pretty much a re-affirmation of your first point.
Individual variability doesn't make people fly. It's reasonable to think there are things no one can do.