The chart above, from Mother Jones, gives a vivid illustration of what has happened regarding income since the Republicans instituted their "trickle-down" economic policy about 1980. Income for the rich (top 1.0%) has climbed, but income for the super-rich (top 0.1%) and the mega-rich (top 0.01%) have grown exorbitantly. Meanwhile, the income for the top 10% has been stagnant, and the bottom 90% has actually lost ground (especially when inflation is considered).
This has caused both the income and wealth gap between the wealthiest Americans and all other Americans to grow to the largest difference since before the Great Depression -- and it is still growing. Very soon, the top 0.1% (about 316,000 Americans) will own more wealth than the bottom 90% (about 284,400,000 Americans).
I don't think that can be justified in a democracy. And I don't think it can be sustainable in a capitalist economy. If we let this continue much longer, both our democracy and our economy will be in trouble. We are fast becoming a nation of rich and poor, as our middle class disappears. Is this the kind of third-world country you want to live in?