You're posing it as an either-or choice between going to Mars and fighting climate change. It's not. Fighting climate change is a political problem. Going to Mars is a scientific and engineering problem.

If everyone had your attitude there would never be any progress. Imagine if someone told Newton "Why are you bothering with how things fall? Go solve the plague or something."

I have no vision of any Martian society. We can figure that out if we get there. Getting there is the interesting part right now.