IIRC when Japan hit that "2X" mark circa 1991 it lead to an economic stall that appears to be permanent. Their economy has been stalled / zero-growth for almost 30 years now. They are cautionary example not an aspirational one.
I do think we need to figure out a “closed system”. Meaning having a throwaway economy isn’t sustainable with a finite earth. Further, it doesn’t seem right to expect every person to have the wits to figure that out, agree with it, and how to properly execute a sustainable life. Ant colonies are clearly not ran by that model. But I also see the resources of space being quite impressive and offering pretty big growth opportunities through just being huge and containing other places for us to setup and live. Though the resources there are definitely prohibitively sparse so they still should be used wisely.
Edit-I also can’t help but wonder where we would be if money value was clearly tied to energy. Oil effectively adds wealth to the economy by literally fueling it. Basing a currency on gold, for instance, sets the pace of monetary growth at the rate of gold extraction. I think oil is similarly pressing upon USD.
Either way it's not a cause of their economic problems, and the doom-mongering around too high a national debt leading to hyperinflation proved to be the exact opposite of the truth - they struggled with deflation.
People are willing to accept living conditions for themselves, especially when they're young that are really not conducive to raising a family.
Many people reach the stage where they would otherwise have children and realize that they just don't want that life in the cramped, high cost housing or long commute times and just don't want to afford a family so they don't.