But isn't that what colonizing Mars is, anyway? Mars has no biodiversity to speak of and won't be a host to ours without significant evolution or resources, so what's the plan there?
Earth isn't just a convenient place to live. It's the only planet we can live on. Until we get warp drive or are much farther along in making a profit colonizing the solar system, not to mention in building better governments, it's just far too early to discuss colonizing Mars. Dreams are great but let's not get blinded by the hopes here. Let's plan a visit, and plan another visit 50 years after that.
Ugh, don't get me started there. Musk wanting to do all these internet satellites interests me but seriously gives me nightmares too in regards to Kessler syndrome.
Maybe someone launches anti-ballistic-missile missiles, and scores a few hits. Debris is spreading to all kinds of orbits. Kessler Syndrome will be the least of our problems as the bombs fall, but it'll be a pain later, after the fallout clears.
It's a lot more difficult to launch through a rock ceiling, radioactive atmosphere, and a cloud of Kessler Syndrome fragments, from a gravity well 1G deep, than it is to launch from the surface of a rock with barely any atmosphere, a bare handful of satellites, in a well only 0.38G deep.
Also, bear in mind that you won't just be stockpiling food, but sufficient biodiversity to reassemble a viable ecosystem, and sufficient industry and education to preserve a viable economy. Otherwise, you still die when the nutri-mat and atmo-pure machines finally break down.
It's certainly easier to dig a deep hole and build a bunker in it, but that expense does not advance the end goal. It is merely insurance against a temporary setback. You still need to establish a launch-capable society on another planet, or everything dies anyway when the sun expands.
Then, after that happens, someone will still be around to say, "It would be cheaper and easier to colonize and terraform Venus than to send generation ships every which way."....