Speaking as a crab in a bucket, for all the very real WorldX achievements there's a certain Muskcrab fatigue if you haven't noticed. He's done enormous job to sour fellow crabs on the idea of leaving this bucket.
Relatedly there are questions about why the whole project seems to assume that it's much more important to preserve the human species, like a celebrated breed of dog, than to protect the lifespans (ideally, healthy lifespans) and welfare of individual human beings, questions which unfortunately can also probably be answered with reference to Musk personally: https://youtu.be/-VfYjPzj1Xw?t=18 .
There's also the wrinkle that if it's viable to send settlers and adequate resupply to Mars, then it's probably much easier and more straightforward to send a few nuclear warheads on their own one-way trip, so the whole premise that a Martian colony wouldn't be struck in a full-scale nuclear war on Earth seems shaky. Now a Martian colony dug in deep under the surface might be relatively safe, but that brings up again the question of whether it wouldn't just be better to build a far-flung network of underground settlements on Earth and/or have submarines loitering in the Antarctic Ocean in shifts.
To your second: there are calamities for which a second self-sufficient planet would be necessary. A large asteroid impact would utterly wreck the global industrial base which is highly dependent on international trade and specialization of resource extraction and manufacturing in different regions of the world, having an independent backup on a different planet is one of the few ways to hedge against this. You could argue that every country on earth be fully self-sufficient and then maybe they could survive but that seems like a much bigger task since you'd be building multiple completely independent civilizations instead of just one. Guarding against another global pandemic is another and being out of range of nuclear weapons and their fallout is a third.
> A large asteroid impact would utterly wreck the global industrial base which is highly dependent on international trade and specialization of resource extraction and manufacturing in different regions of the world
That's economic collapse not extinction level collapse, space based mining might help with that but it's not the kind of event that actually makes a self sufficient
> Guarding against another global pandemic is another
This kind of presumes a very low level of travel and trade between Earth and Elsewhere which is extremely unlikely per problem 1 and the fact they'll need some economic reason to exist, at the very least they'll have to make money to buy the necessary items from Earth they cannot produce locally.
> being out of range of nuclear weapons and their fallout is a third.
This goes back to the actual thing I was talking about even a heavily bombed out Earth is hundreds of times easier to survive on than Mars or any given asteroid. Hence any tech that makes those places survivable make even the most damaged Earth also survivable.
Global economic collapse due to an asteroid or nuclear war might not cause human extinction but it would mean a very large regression in our technological capacity. That could endure for hundreds if not thousands of years. Maybe we would never fully recover, people argue that point based on all of the easy to access resources having already been exploited though I have more faith in humanity's ingenuity. The role of a Mars colony in this scenario isn't to send iron ore to Earth, it's to maintain high technology and continue moving forward.
The risk of a pandemic becoming interplanetary is much lower than the risk of international spread. Travel between Earth and Mars is necessarily constrained by their orbits with a window opening only every 26 months. Most travel would likely be uncrewed cargo and when people do make the trip there would be strict quarantine measures taken (this is already done with current crewed launches to orbit and there is established history of immigration being subject to quarantine). Most importantly, the trip to Mars takes much longer than the incubation period of any disease likely to cause a pandemic so the disease will have run its course by the time the ship reaches Mars and they can decide what to do at that point (at the extreme they may resupply it and send it back but that's probably not necessary in most cases).
My concern is the incentives and economics that make it possible for them to exist, principally (relatively) cheap launch and transit costs, preclude it ever being economical to invest the resources required to ship say modern chip lithography equipment out to the new colonies rather than them continuing to buy them from Earth. Or the alternative, they get treated like pre-revolution US colonies and are intentionally kept dependent by restrictions on imports and tech exports in order to provide a market for the mother civ to sell into. And this time instead of being in a verdant land full of resources the colonies are on baren rocks dependent on the mother country for critical life support supplies so the capture and dependency are magnified and much stronger.
I don't really see the point in arguing against it. If a private company and private individuals want to try to colonize Mars then what does it have to do with anyone else? You can't cling on to their legs and scream "don't go!" It all just seems to be in the same vein as that famous headline saying man will never fly.
Yes it wouldn't be the first step on establishing them but it is the kind of things it would need to be truly self sufficient. Chips are in practically every thing today already, it's a critical supply component to do anything other than simply surviving.
It's silly to me that some crabs are working on trying to leave the nice bucket (me, where all the crabs are) for some shoddy bucket far far away. All because they don't want to fix the bucket they have at hand.