The 1%

You forget one important   reason for the stability of the US political system: a sizable and constantly growing middle class.  The size  and wealth of this    stabilizing buffer of society has been shrinking  since the 80s. The GDP per capita has doubled, but it has not  doubled on all capita. For most people (most= more that 50%)  the GDP on their capita has actually shrunk.    Clearly   the past three decades have witness a reallocation of this country wealth on an unprecedented scale. You ask "why shouldn't the top 1% have 40% of the nation's wealth? "  The answer is very simple: it is for the same reason why the top 1% should not own 99% of the nation's wealth.    The fact that the  upward mobility in US is below that of Europe  should worry people. And the great equalizer, education, is becoming  a  heavier burden on  most  households.   At some point markets need  a correction to   help maintain that which is  vital in a free market: fairness of competition.   That is why monopolies  were   destroyed, not by the will of the markets, but by the will of the people,  that is why insider trading is punished.  That is why a minority  owning  a large chunk of the  wealth can rigg the rules of the game  to  their will,  to the point that if your're born  on a wrong zip cote, "the shining city on the hill" will only be a postcard image for you.