Yet all our ancestors have survived. I don't see why we, who are considerably more intelligent, who can predict celestial events, who can store food and water for years, who can build nuclear-bomb-proof bunkers, can generate energy from urianium dust, would do worse a job at surviving than tiny mouse-like animals 65 million years ago.
Having a Martian society existing concurrently is like the difference between saying "yeah, we could back up our server to tape" and actually running concurrent instances. Or like the difference between legislation to require eco-friendly behavior and technology that makes eco-friendly behavior more economical than the old way.
It exists not as a resource drain but as an improvement. Useful things that happen to also solve problems are often superior to perhaps less expensive things that solve the problem but might be seen as a cost center.
Also, I don't disagree that post-apocalypse, 99% of those Martian manufacturers of orbital solar collectors should hop on the next shuttle back to Earth.
I wonder what you would have posted if they hadn't.
Also not saying going to Mars is necessary, just pointing out that it seems that's Musk's thoughts on the matter.