Sadly what I know of humanity tells me that we won't do that without ruining it to drill for resources like oil, so I say let's leave at least one place untouched back here on earth until we have a backup plan somewhere.

Who knows! Antartica used to be super moist and wet, so the oil resources may be there. I mean, if you can find a way to get under the mile of ice, there is likely to be a lot of resources just sitting there for the taking. It is an entire virgin contient afterall.

There isn't the forcing function of being really hard to get there, so it doesn't interest people to build self contained habitations on earth. It was tried a few times without much success, for example with the Biosphere project.

To be fair, Biosphere was a bit of a planning disaster. It was not meant to be a trial run for a self-sustaining greenhouse per se. It was more of a 'save the earth in a nano-way' project. They had a rainforest section, a desert section, etc. They did learn a LOT about plant biology, weather interactions, and microbiota, though mostly via failure, which was still SUPER useful.

However, just building something like Biosphere was incredibly difficult and laor intensive. Trying to do that constuction on Mars would be a LOT more difficult still.

https://en.wikipedia.org/wiki/Biosphere_2