I remember some discussion of this in Kim Stanley Robinson's "Green Mars", IIRC: he points out that it's simply too energy-inefficient to ship a few billion human beings out of Earth's gravity well, and no extraterrestrial habitat will have an ecosphere anything the size of Earth's.

Earth is simply the best place to support humans in the galaxy, and it needs to be sustainable in its own terms. We can and should live elsewhere, but that doesn't mean Earth will be any less important to us.

Regardless of where people venture out in the solar system, the folks back on Earth will have to operate within their resources, right?

Yeah, I doubt someone with a sustainable habitat on Mars, and enough resources to send some back to Earth, is going to just send them without getting paid more than it would take to claw them out of the ground on Earth in the first place. It would make more sense to just keep the resources on Mars where one can use them, rather than wasting 95% of them transporting 4% to Earth.

Who gets the mandatory ticket out? Who gets to stay and enjoy Earth?

Granted, I don't even want live anywhere on Earth. I would like a temperate place with good food, culture, infrastructure, sea is a plus.

The 60's idea was "we can make other planets exactly like Alabama", but guess what, not many people want to move to new Alabama.

Establishing sustainable colonies off Earth would put some of our metaphorical eggs in another basket, and make it more likely that our species could survive a major catastrophe. It's something we should be able to do in the next few decades or centuries, and I'm all for it.

But given current or reasonably foreseeable technology, we're just not going to be able to ship off enough people to relieve population pressures on Earth.

(Question: Has emigration to North America ever made a significant dent in population pressures in Europe, Asia, or Africa?)

You saw the movie Elysium right?