As far as what to do about it? The only solution could be to break up Amazon, Google, Apple, etc. Taxation is not it. The Federal government and the Fed controls the money printer and influences how high these stock valuations are getting. They're a large part of the problem.
We can't print trillions of dollars without side effects in supply, demand and price mechanics. In this case, dollars are chasing productive growth assets as yields in bonds hit the floor and go under zero in some countries.
The growth in inequality correlates with the growth in the national debt, and monetary supply growth.
