We humans usually don't focus our resources on a single issues. Have you ever heard we have to stop spending money for cosmetics because right now we have to fix amazon deforestation? And even then, we usually don't go all in on a single plan but want backups. Mars might be one of those. A tiny one we barely invest any resources into. NASA is ~0.5 percent of the US budget. Cosmetics would be easily 3x that.

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.