>If we really want to escape our fate on earth, well we could simply take our time to slowly develop ways go to space. Assuming that it is possible for humans to reach anything beyond the solar system, which may not be the case. There are practical physical and thermodynamic considerations that may prevent us from ever colonizing much in space, even if we were to try hard. In which case, preserving earth would not just be the best thing to do, it would be the only thing we can do.
Ultimately it's a moral judgement. The people living now are different in one key way from people who may exist in the future: they exist. At the core of economics is fulfilling peoples' revealed preferences. If peoples' revealed preferences show they prefer greater consumption now at the expense of people who may live in the feature, that's what will be optimised. What weight should the potential wishes of people potentially born in the future have compared to those of people actually existing now? That's ultimately a philosophical questions, outside the range of economics, maths or science. The one thing that economics shows is that the collective preferences of people existing now tend to put a lot more weight on the importance of people existing now than on people who might exist in the future.