'Mankind' as we know it today will never travel between stars, for the reasons mentioned and a dozen more. But there's no reason to presume control over our biology and psychology won't advance enough we might overcome the vastness of space.

Fundamentally, though, is the truth that if we can control our biology enough to overcome its marriage to gravity, we will no longer be the creatures we are now. The same reasoning applies even more to our psychology.

The human beings who visit another star, or even those who visit the more distant planets, will be changed beyond recognition if they are to survive the journey. But that doesn't mean we aren't capable of such change.