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the number of individuals who actually pay the estate tax is pretty lowA paper published in 2000 "began with an aggregate time-series analysis, and found that summary measures of the estate tax rate structure are generally negatively correlated with the reported net worth of the top estates relative to national wealth," which "is consistent with estate taxation reducing either wealth accumulation or inducing avoidance, or both" [1].
The simplest strategy for avoiding the tax involves gifting. "A couple with two children could divest itself of $1 million over a twenty-five year period simply by taking advantage of the gift tax exclusion" [2]. That grows if the couple contemplates gifts to grandchildren, spouses of children or grandchildren, et cetera. Another involves the "diversion of profitable investment opportunities" to heirs, e.g. by "arranging profitable business deals and then bring[ing] their children in as coinvestors". Lending to children at prevailing rates and guaranteeing their loans are related strategies. More sophisticated techniques include "preferred stock recapitalizations in closely held firms, installment sales, and life insurance."
TL; DR The estate tax does little to reduce inequality.
On a more meta level, it is interesting to observe that for "several decades, total revenues raised by estate and gift taxes have roughly equalled those raised by excise taxes on alcohol and tobacco" [3]. The estate tax attracts attention because of a fundamental disagreement, regarding taxes, in our politics.
"Broadly speaking, the tension is one between a desire for structural tax reform, which would move the tax system to- wards greater horizontal and vertical equity, and a desire for tax provi- sions designed to stimulate increased savings or capital formation. This tension produces a direct conflict between the need to tax capital or the income from capital in order to achieve a progressive tax burden and the perceived need to exempt capital and capital income from tax in order to induce economic growth" [3].
[1] http://piketty.pse.ens.fr/files/KopczukSlemrod2001.pdf
[2] http://www.nber.org/chapters/c10931.pdf
[3] http://digitalcommons.law.yale.edu/cgi/viewcontent.cgi?artic...