These are not mutually exclusive things. The primary reason cited for the desire to become multi-planetary is to use other planets as a escape hatch in case something happens. And they are incentived to escape themselves and leave others here to rot. It's much more efficient than trying to save one planet from armageddon every time.
It's actually not. If we can't figure out how to live here, we aren't going to figure out how to live in a less hospitable environment.
In the best case scenario, we go to mars and do the same thing again. That's disregarding all the actual problems it would take to get there, and live there. And also disregarding all the problems we actually HAVE to solve about living here (and living, in general).
Spoken like a true colonialist! ;-)
It's that level of evidence.