I used to be of the same opinion as you, but there are actually some good counter arguments:

1) Two week day/night cycle: This means it would be hard to power your base with solar energy. You'd need massive battery banks. Or another power source. You could try nuclear, but cooling might be a challenge without air or water. Mars has a slightly longer day than earth, which makes solar power much more viable (though solar insolation is less than on earth)

2) No atmosphere, so all Oxygen has to be brought in (unless we find it somewhere else on the Moon). Also any carbon needed to grow plants needs to be brought in. Mars has a thin atmosphere, but we could get Oxygen and Carbon from it.

3) It's not clear if we can find water on the moon. Mars almost certainly has water underground, and for sure at the pole.

4) The lower gravity might have long term effects on humans. Though to be fair, we don't know if Mars gravity will be harmful as well.

Ironically, a lot more on-the-ground investigation has been done on Mars than the moon. I suspect there's a lot more useful stuff waiting to be found. All we've looked at from the moon are a few pounds of rocks from a handful of sites.

Why not have both? :) as far as "backup of human civilization" goes though, Mars has more potential: water, atmosphere (thin though it may be), higher gravity, and a day similar to earth. If the s ever htf on earth, a mars colony has a better chance of surviving one day without earth's help.

I guess for me the question is if that will matter or we get strong AI first.

> so why not be a couple days away rather than a year

Hm, maybe because you'd get twice the gravity and a "day" that lasts closer to 24 hours than 24 days?

Does the diurnal cycle matter if you must stay within a shielded dome?

Lower gravity doesn't matter as much if you can be regularly cycled back to earth.