How is that a fundamental insight of economics. It's the insight of the smallest group all the way to cities and civilization. Self interest, by definition, motivates cooperation.
> From this traditional perspective the "common good" is a result of insufficient property rights: if everything is owned by something, then by everyone looking after their private good, everything will be looked after (because all "common good" is somebody's "private good").
What you are describing isn't "insufficient property rights", you are describing "insufficient property".
> It also ignores that redistribution results in less "private good" (GDP) for everyone, because by definition it's taking wealth from people who on average have demonstrated more ability to grow wealth and giving it to people who have demonstrated less ability to grow wealth.
Wealth is always "stolen". Behind every great wealth is a great crime. Wealth is generate by theft of assets ( land, oil, resources ) or theft of labor. Bill Gates didn't generate his wealth. His workers generated the wealth, he and the shareholders just siphoned the largest part of it. Look at the fundamental wealth of the US - the land and resources that provides unimaginable amount of wealth. All stolen from the natives.
Wealth = clever robbing the less clever with the protection of the law which they created. And it isn't necessarily a bad thing.
> If they both start with the same endowment
What an ideal world you must live in.
> More practical example: imagine if after Paypal, Elon Musk's entire wealth had been redistributed to all Americans.
Who is even advocating for taking all of anyone's wealth?
> and the world has no Tesla or SpaceX.
Why not? Using your argument, PayPal couldn't exist since Musk didn't have that PayPal money to fund his business.
You have an agenda and you are using obvious extremes and lies to push your agenda. The other side does the same. Instead of being driven by agenda, try to think objectively. Look at the problem from afar.
Extremes in either direction is bad for the individual and society.