Only a human could look out into the night sky and come up with the idea of owning it.
There is almost infinite space for us, right here on our planet, even if our numbers become almost infinite...
Lao Tzu speaks of The Master as being content to remain where he is, all the days of his life, without the need to go anywhere else. He can do this because he is content, and at peace. I have discovered his words to be true: having been a great explorer and adventurer, always needing to discover places new, now I rarely feel like going anywhere else. I have no inclination to travel.
Combine that with the almost-reality of being able to absorb/manufacture all necessary nutrition from sunlight and oxygen, which spiritual adepts have always been able to do, how much space does humanity really need?
The most important thing - far more so than migrating to the stars - is to become appreciative and responsible for the environment we were born into.