I think most of the appeal of going to Mars is a sense of "starting over" and or course not bringing "them" with, for your favorite definition of "them".
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.