What makes Mars colonies (and moon colonies) interesting to me is a recognition that recorded civilization is only about 12,500 years old. That prior to that the entire planet was experiencing an ice age which lasted ~100,000 years, and prior to that people were already "behaviorally modern" in ways which left impressions in the archeological record.
This suggests that our home planet could have a meteor or ice age shaped surprise for us any moment, and that it might not be a bad idea to have remote backups.
I also think that working to live somewhere other than Earth will teach us much more about exactly why and how Earth is special.
Living on Mars, on the other hand, will require a much higher degree of dependence on others as there are no woods, no food to hunt or farm, and nothing but rock from which to make necessities. Colonizing Mars or a moon will require a great deal of interaction with all the social and technical constructs that anyone wanting to "start over" is seeking to distance themselves from.
I only say this in case we weren't clear on each other's scale argument. Building a cabin and going for a hike is very different from building a new society from scratch. I do think both are desires but the second is the one I'm talking about.
Give those ideas a run, and then you've made a compelling case for subsidizing and bootstrapping the move of dirty heavy industry and mining off-world: metals from the asteroid belt, manufacturing in high orbit - the ecological science to make it more sustainable.
You then also get some economic benefits once you're up and running: off-world industry would find the products of the biosphere very valuable - more so then anything so simple as oil, metal or refined chemicals. Putting a distinct price on keeping the Earth's biodiversity alive and protected because people want to be able to buy "live soil" - to borrow from the expanse - would put us in a much better long term position as a species.
No one believes that mars is going to be a better/easier place to live than earth. It's idiotic, and only spouted by people that don't like the idea of Mars, and said to make "marsers" look like idiots in association.
The chief value of Mars has two parts. First, it opens up the first true frontier we’ve had in over a century and could serve as a sort of societal pressure relief valve. Second, as soon as there’s people living on Mars the impetus for developing technology to make living there (and in space) more safe, sustainable, and comfortable increases dramatically, which is a critical step in achieving true mastery of human spaceflight and ensuring that the species is not forever stuck in the bottom of Earth’s gravity well.
Some may argue that the moon can serve these purposes as well and that may be true to a degree, but its proximity is a liability. Moon inhabitations are close enough to be well within the sphere of Earth’s political influence even if it achieves self-sustainability, which itself is unlikely because Earth is always there as a convenient source of supplies and escape hatch, just a week away. There’s a certain level of necessary commitment and autonomy that comes with building a civilization on Mars which I believe is key.
People need to believe that the future will be better than the present, especially when the present sucks. If you don't have that, what is there?