Ok, I'm following the thread continued here.
To colonize the galaxy will take far too long for us, humans. I'm sure we'll need successors of another kind to spread our memories, our cultures, our humankind all over the universe. Humans only last less than a century and are built for the 1G gravity of our planet, breathing the air of our planet. If we want to leave our planet, there are many worlds within our solar system, but none are suitable to our kind of life. Closed ecological systems can exist, but with a huge emphasis in control, safety, closed environment, and thus severely restricted freedom. Colonize other star systems? Here, already, the distances are completely incompatible with our human limitations.
The solution would be to commit mankind's future to another kind of "consciousness". There might be a great reluctance towards this, but I'm pretty sure anyway that mankind will become extinct long before our Sun becomes a threat.
And let's suppose we do have a successor for whom a world with oxygen, 1G, water is not less hostile than a totally airless asteroid or even vacuum.
Why colonize anything, in that case?
To colonize a place means to live there and use the benefits found on the spot.
If our successors can go anywhere and feel no less at home there than here, they won't need to colonize!
Raoul