[DarkTree]

I'm kind of playing devil's advocate here, but I think there are some key differences with your analogy.

The goal of colonizing another planet would give a small subset of people the ability to continue living if the people on Earth were to destroy themselves. This is a hypothetical situation that -if it happens- will kill off almost everyone, dragging hopes, dreams, money, infrastructure, standards of living (basically everything that makes life enjoyable) with it. So if that is destroyed, why does it matter if humans continue living as a species? Especially on an extremely harsh planet.

Your analogous examples differ because all of those things -medicine, quality of life, children, even sustaining our environment- help us now. We do those things to make our own lives longer, improve our own children's lives, and make our quality of life greater, not some hypothetical future civilization away from Earth. You're right that humanity's best interest is survival, but I think way more people are concerned with their own survival and I think that's where the true incentives for those examples lie.