Gary Becker notes that wealth disparity has actually

shrunk in the last century:

Given the enormous wealth of these individuals, it might be surmised that the gap between the incomes of the very richest and the average individual increased substantially during the past 100 years. Actually, the opposite appears to be true. John D. Rockefeller's income was about 1/3 of 1 percent of the much smaller American GDP of his time, whereas Bill Gates' income is less than 1/12 of one percent of current US GDP. More generally, the overall inequality in wealth also declined greatly in the US, UK, and other western European nations during the first 60 years of the 20th century. Inequality has increased significantly since then, but it is still less than at the beginning of the century.

He also points out, in taxing the wealthy, there is no free lunch:

The US imposes a 45 percent tax on all (taxable) estates above a few million dollars. This tax yields a moderate amount of revenue, but at the cost of creating a large industry of highly skilled estate tax professionals who would have used their talents at more socially productive activities were it not for the demand to find loopholes. One justification for such high taxes that has some appeal even when only modest sums are collected is that high taxes have encouraged the very wealthy to create large tax-exempt educational and charitable foundations in order to reduce their taxes. Yet since Rockefeller, Carnegie, and other highly wealthy individuals also created foundations when estate taxes were low, it is not clear how many modern foundations have been created mainly to avoid these taxes. In any case, larger foundations could still be encouraged with much bigger exemptions from the estate tax-perhaps $50 million or even more. This tax should only affect the extremely wealthy.