Well the Pope is right. From a religious standpoint, it is entirely un-Christ like to amass so much wealth that you could never use or donate all of it. Wealth is not a virtue in the Christian faith, and single-minded pursuit of ridiculous wealth is not a valid Christian calling. There is also the fact that there is not such thing as a "clean" billion dollars, much less a trillion. Huge fortunes are built on moral compromise at best, and outright evil at worst.
From a societal standpoint, that much wealth is a hugely destabilizing force. There are many kinds of power in our society, but political, economic, and military power are the most important. We limit our military power by making it subordinate to political power. We would also never tolerate a private citizing raising an army and buying military hardware while in our country. We limit political power with check and balances, the Constitution, and the Bill of Rights. We don't limit economic power at all though. Any corporation or individual can amass as much economic power as they want. When you have limited military power, limited political power, and unlimited economic power, then it's not hard to see that economic power will dominate. And it's been proven that economic power dominates political power. The richest people get all the laws passed they prefer, while popular support has no correlation the passing of laws. That's good if you want a plutocracy I guess, but it's doom for any other sort of society
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