If we ever find ourselves in a situation where we cannot survive on a planet where food literally grows out of the ground, with abundant liquid water and atmospheric oxygen at 1 atm, how on Earth would we survive on a planet that is devoid of life, has no liquid water, an atmosphere that's 1% the pressure of Earth's with no atmospheric oxygen, and little to no sources of energy?

Again, the bottom of the ocean is far more habitable than Mars, even if we experienced a similar extinction event similar to the one we experienced 65 million years ago.

Earth is habitable now. There are plenty of plausible non-anthropogenic disasters that may make that so not so. Some typical examples include megavolcano eruption, coronal mass ejection, and asteroid impact. It would be good to not have all of our eggs in one basket here on Earth.

And it's for exactly the same reason of having redundancy that it would be a good thing for Earth to continue to remain habitable, i.e. we should stop ruining the planet through climate change.

It's not a moral hazard at all; the two outlooks are congruous.

Even after any of those events, the bottom of the ocean would still be more habitable than Mars.

> It's not a moral hazard at all; the two outlooks are congruous.

The moral hazard is that we'll begin to think of Mars as a backup, when it isn't one at all. The Earth is very likely to be the one shot we have at a home. If we can't manage to make Earth habitable in the face of catastrophe, there is little hope to make a cold, barren rock that's millions of miles away habitable.