Apart from proof of concept I just don’t see any practical reason to colonise mars.
First: how awful would you consider a world-wide apocalypse to be, where the human race is effectively ended? Let’s call it massively, enormously bad. How likely is it that that happens? Well, probably incredibly small, but not zero. Multiply the two together and you’ve got a weighting for how much we should care and prepare. In this case, the incredibly small probability is likely balanced by the enormous awfulness - meaning some level of reasonable preparation for existence beyond Earth makes rational sense.
Second: think a thousand years into the future. Do you imagine that humans will be still only on earth, or will we have reached out and explored further - beyond our planet, beyond our solar system? If you can imagine any version of ‘beyond Earth’ - then Starship and Mars might represent the first baby steps needed to ultimately achieve that outcome.
The bigger benefit is how it gets the ball rolling on development of all the technologies associated with keeping humans alive and thriving in space and on the surfaces of other bodies in a way that the moon can’t.
The problem with the moon is that its distance. It’s convenient, which means that doing anything there isn’t much of a commitment and thus, can be canceled and forgotten about on a whim. It also means that there’s not much pressure to make human presences there self-sustaining — worst case scenario, another rocket full of supplies and/or personnel is only a week away.
A presence on Mars on the other hand by nature has to be something less frivolous. You have to plan to be there a long time no matter what, and from the moment the first crew’s boots touch the ground they’re going to be pouring themselves into becoming self-sustainable. The nations and companies behind the project can’t so conveniently pull the plug. Once it’s there, everybody involved is in it for the long haul and the longer it exists and more it grows the harder it is to back out of.
So I guess more than anything, out of the destinations that are being seriously considered by NASA, SpaceX, etc, Mars is the best at providing some kind of insurance against stagnancy and malaise in the crewed space program like we saw from the late 70s through 2010 or so.
Another global airborne pandemic, but this time with a much higher fatality rate?
I mean, isn't the whole vision that rather comfortable and fast ride, like in an airliner, but the duration of a cruise? Without all that quarantine shit?
Do you expect the masses to mars movers to be left alone unattended after reaching their destination, no maintenance, except under BSL-4 conditions, for being ready to go back?
Or the passengers showered and scrubbed in airlocks with antiseptic foam, ultraviolet light, and whatnot else, while their clothing is being 'recycled'?
The airlocks probably will be there, but the rest? One could probably argue that it all won't matter, like it mostly doesn't in Antarctica, because air too dry and cold, etc.
But can you be sure?
A useful asteroid mining base might eventually let you expand into the Oort cloud and then colonize the rest of the galaxy assuming they could be 100% self sufficient and didn’t need solar power. But even here the hard bits are 99% technology we could develop on earth for other things like fusion power.
And that is just one apocalypse variant. Nuclear holocaust. Antimatter bombs. Possibly even a massive gamma ray burst, are all safe from Mars even if they might kill everyone on Earth.
Our species took an incredible amount of time to evolve, likely long enough to not re-appear in this solar system if lost. Which is a very weird point for me feeling that I have to argue for lol
Elon often talks about how exploration is exciting and inspirational and a prerequisite for future interstellar travel, and that works better as a justification to go to Mars, IMO. Also, while those disasters might not completely wipe out humans on Earth, they could reverse centuries or millennia of progress and delay further space exploration for hundreds or thousands of years if we don't do it now while we have the chance.
From what I understand, for a nuke war, it is still _possible_ it will take out everyone considering the nuclear winter it will cause. In my thinking a redundant colony is worth even saving us having to play existential Russian Roulette with one loaded.