The complaint at issue is that a passive investor who happened to have 10 million dollars that they inherited at 30, sticks it in betterment for 50 years while drawing a top 1% of income 380k for expenses ( accounting for tax rate ) will eventually have 130 million dollars. They can easily pass this amount down to children at estate tax rates to enable the next generation to do nothing as well, or they could use any one of a number of tax sheltering methods to avoid or defray the estate tax as well.
Generational wealth, or "idle wealth" has been a concern in the US from Thomas Jefferson onward - capital gains taxes are merely one mechanism to restrict it.
I'm not wading into that debate. I'm just concerned with accurate use of terminology, as multiple people in this discussion seem to be playing fast-and-loose with it.
Capital gains are income and reported on Form 1040. What they are not is "ordinary income" subject to the income tax table. A person with $700k on capital gains is well inside the top 1% of income.