Nah, your imagination of the horrors that nature can (and did) unleash upon the Earth is pretty limited. A Theia impact would make Earth far less livable than Mars. Would sterilize the planet.
And you hit on a good point in your last sentence: Developing a self-sustaining civilization on Mars would PROVE we can easily be sustainable on Earth.
And you hit on a good point in your last sentence: Developing a self-sustaining civilization on Mars would PROVE we can easily be sustainable on Earth.