Humanity's only goal, in and of itself, seems to be to
survive and reproduce. Both on a micro and macro scale, this is the behavior we see all of
humankind exhibiting. Given this, it can be safely assumed that anything that allows more humans to survive, and survive more comfortably, is a step in the right direction. Ergo, we should
expand wherever possible.
I don't think many people would argue, judging from mankind's past, that human beings are
expansionists. Starting from one small area on the
planet, we've been slowly and steadily expanding until we cover all hospitable regions and semi-hospitable regions on the
globe. Assuming we, humanity, can clean up our act and solve our more local problems (like
war,
famine, and so on), I see no reason why we shouldn't continue to expand; in this case, to other worlds.
Being spread through multiple planets and hopefully, systems, will greatly decrease our chances of being entirely wiped out by some large-scale natural disaster, such as a rogue
asteroid or future unforeseen sun behavior. It can't hurt to spread out a bit.
The disappointing conclusion is that we're currently very limited by our technology level, and space-based
research is progressing very slowly. Well, here's hoping.