I don't expect that colonization of Mars or other distant places will save "us", but it might well save many of those who go. There are lots of ways in which places on Mars are less hospitable to human life than places on Earth, but if things get really bad on Earth, the surrounding weather will not be nearly as bad as how other people are reacting.

Area denial isn't just about land mines. It can mean fomenting political unrest among the constituents of a standing, stable, and sustainable Martian colony, so that it's suddenly an unappealing alternative to solving Earth's problems. Don't go there, it's the Salem witch trials and the holocaust all at once. Stay here and fix the biosphere instead.

Eventually the situation will be come obvious enough that it can no longer be ignored by half of the West, and most of the developing world.

When that happens, and a solution to the problem becomes a global priority, it will be solved in one manner or another.

The closer we get to that point, the worse it will be for those further from resources (political and financial).

I'm with your GP on that. Not terra-forming, but a small mars colony will prove Humans are able to live independent from earths ecology. That we have the necessary technology and just have to scale it up. That will be hard enough on potentially short available time frame we have to react, so doing the R&D now in form of a government financed space program will probably buy us necessary time.

That doesn't mean the colony has to be independent of earths economy. Decoupling mines and factories from earths ecology will be a lot easier than doing so for e.g. food production.

But yeah, that will be painful and I'd prefer mankind to find ways to keep our current environment intact.