It is a false choice that we have to protect this planet OR work on the technology to move elsewhere. It doesn't have to be either or. In fact, right now even it isn't. We're putting effort toward both, but the amount spent on moving to another planet is so little it is practically rounding error, so really we are putting effort toward preserving this planet and not moving when looked at through that lens.

There are, however, problems outside of human-made pollution that threaten the planet. Asteroids aren't fiction. The one that was famously recorded in Russia a few years ago shattered windows, but if, by chance, had impacted at a different angle we would have been looking at a crater in the ground and we'd probably be discussing increases to the asteroid defense budget on Hacker News today still. Historically we can see the effects of the asteroid that caused the K-T mass extinction in a variety of places. Reducing, reusing, and recycling won't help us in the cases of stellar-based threats like large asteroids, a field of millions of smaller asteroids that gets captured by earth, or some, as of yet, barely understood phenomenon like a hypothetical traveling black hole or radiation burst of some kind.