In a simulator, could you have 12 billion people with their needs met, living fulfilled lives and continuing into the far future? Yes.
Is there a political and practical way to reach that state? No. "One study estimates it would take just over 5 Earths to support the human population if everyone’s consumption patterns were similar to the average American." Any US government that tried to bring America's environmental footprint down to a sustainable or fair level would be voted out. It doesn't matter whether it would be gas taxes, meat taxes, per mile taxes, flight taxes, carbon tax and dividend, building renewable energy in less developed countries, or any other scheme. It doesn't matter if it was targeted at the ultra rich or the middle class. The sheer scale of it would cause Americans to vote out the government. And the same is true for any democracy and plenty of the non-democracies too.