Capitalism has created more wealth than any other political system in history. The US started out as a capitalistic society. It has been degraded and attacked since the beginning and now is far from capitalist.
On the contrary, the modern United States is the purest distillation of capitalist society since the gilded age. If you don't like what the USA has become, you don't like capitalism. Accept it.
His main thesis is that the return on invested capital increases faster than the general growth of the economy, leading to increasing inequality (because those with capital to invest get richer faster than the rest). To begin with, he confuses return on invested capital with the growth rate of capital of corporate profits - a mistake that is unforgivable even for a 1st year graduate student of economics.
If this is confusing and frustrating to you, it's because you don't understand that
economics is a pseudo-science. It exists solely to support and uphold the cult of capitalism.