The only thing that I can think of to make Mars a better option than Earth is if Earth is struck by some truly gigantic asteroid. But it would have to be big en

The only thing that I can think of to make Mars a better option than Earth is if Earth is struck by some truly gigantic asteroid. But it would have to be big enough to seriously damage a 1,000 trillion metric ton ball (we'll take it as given that the Earth isn't flat) of iron. Merely stripping the atmosphere wouldn't be enough - you need to fundamentally compromise the structural integrity of the planet to make it as unlivable as Mars.