Don't you think that the problems with the environment sort of stem most significantly from emergent social phenomena analogous to (but not exactly the same as) such things as tragedy of the commons? It's not like this version of the human race just got lucky and got all the bad 'uns. Humans are humans, no point in bemoaning reality. But the social structures are in a sense an equally root cause.

I would say, yes, the economic theory of the "tragedy of the commons" is a major part of the issue. Good thing that the modern counterparts to those theorists have come to understand that the solution to the tragedy of the commons is to ensure that the costs of the consumption are borne by the consumer.

Regulation, societal norms drafted from the start to ensure transparency, and the "greater good" spirit that, one could easily argue, would be prevalent in those who would choose to risk their lives to leave this rock behind... all those things would form the framework by which our offspring would ensure that they're capable of learning from the mistakes of their forebears.

I believe that, as a race, we're too late to undo the damage we've done to our environment. The patient (our way of life) is terminal, we can only hope to make ourselves comfortable in our waning years without unnecessarily spreading the disease.

But, as cliché as it sounds, I am not hopeless, and I simply cannot allow myself to believe that future generations would do the same thing if they had another planet - or even this one - to start over again. I MUST believe that part of the human condition includes learning from and not repeating the mistakes that cost billions of lives.

OK so what disqualifies a polluter with a pile of cash from buying a seat from one of these kids?

I see the whole problem as related to manifest destiny, either economic or religious. Pure free markets will save us, and/or so will some deity. Because such faith can't possibly be wrong, can't possibly lead us astray to the degree the species ends.

Is that so?

I don't think a deity or a politician or a wealthy philanthropist will save us. We're beyond saving. I think I can teach my kids how to help save themselves and their like-minded peers, those very peers that would leave this planet behind if they could.

As for what stops someone buying a seat on that one-way ride to a brave new world? Two things:

1) Your hypothetical buyer isn't actually that brave.

2) The same reason people can't rush the cockpit of a fully loaded airliner any longer. The rest of the passengers know it's in their best interests, as a group, to prevent that from happening.