What could possibly make Earth as uninhabitable as Mars, without destroying Mars as well? And why not invest in technology that could keep people alive on Earth in Martian-style conditions (without all the extra problems of logistics and low gravity)?
Let's first create a self-sustaining vault that can house a million people for indefinite amounts of time on Earth, and then let's revisit sending humans to Mars with all the new technology we developed doing so.
In the meantime, let's actually spend space program resources on actual useful exploration, such as finding out if there is life on Mars or on other liquid-water worlds in the Solar System (such as Europa). Confirming or denying this would be a much much much bigger boon to scientific understanding than getting an ISS-style outpost to last a few years on Mars, and it would also be far cheaper.
What could possibly make Earth as uninhabitable as Mars, without destroying Mars as well?
Almost nothing. I agree the Mars colonialization idea is absurd in any foreseeable timeframe. My point is mostly fantasy seems serve to numb people to the damage to Earth that's now going. If someone is worried about the future of the human, they should be working on climate change. Especially if they have enough money and influence to make themselves widely heard, as do many of the people hocking the Mars-boondoggle.
The odds of a storm of asteroids hitting Earth are pretty much the same as them hitting Mars. Except the atmosphere protects us against smaller asteroids, where they burn up in the air and on Mars would impact the surface.
The chances of humans surviving on Mars after such an event is extremely less than humans surviving on Earth. We know the Earth has remained hospitable to life after many instances, Mars hasn't been hospitable to complex multi-cellular life in its entire existence, or at least the last billion years or so.
Even if the worst case events were definitely going to happen tomorrow (killer asteroids, Yellowstone erupting, massive airborne contagion) I would still rather be on Earth than on Mars. Earth is more habitable before, during, and after these extinction-level events than Mars is on Mars’s best day.
Let's first create a self-sustaining vault that can house a million people for indefinite amounts of time on Earth, and then let's revisit sending humans to Mars with all the new technology we developed doing so.
In the meantime, let's actually spend space program resources on actual useful exploration, such as finding out if there is life on Mars or on other liquid-water worlds in the Solar System (such as Europa). Confirming or denying this would be a much much much bigger boon to scientific understanding than getting an ISS-style outpost to last a few years on Mars, and it would also be far cheaper.