>However, the period of the fastest economic growth in the US (1940-1950s) featured much higher taxes, much lower ratios between the highest and lowest paid, and much more economic equality.
This is a much parroted line, but it needs to be pointed out just how exceptional of a time period the 1940s-1950s were in the history of the world. The US at this time was literally the only functioning industrialized economy left on earth. All of Europe, Russia, and Japan were left in ruins. China hadn't even remotely begun to industrialize. Southeast Asia, Africa, and Latin America's GDPs were totally negligible. If you wanted to buy anything beyond raw materials, it came from the US.
We live in a fundamentally different world now, where we must compete in a fully globalized economy. The US has succeeded at competing in high paid, high technology sectors, which by their nature have contributed to the inequality of incomes we now see.