A 100% death tax would be efficient as well as fair.

Billionaires are not socially productive. They can't even spend their money to enjoy it: their consumption is a rounding error on their wealth. So making them pay it as tax to the state hardly changes their well-being. The same applies to their inheritance. It's true that taxation creates a disincentive, but in this case, the disincentive to making billions would be more than offset by the incentive to give it away. Taxes on billionares or inheritances are therefore highly efficient as well as fair.<br><br>&#x200B;<br><br>Edit: if death taxes are so good why are they rare? It's worth noting that the original philosophy of the USA was to avoid aristocracies. The largest wealth creators of the 19th century were also critics of inheritance ("the bequest motive" was one of the reasons Keynes didn't like unregulated capitalism). The largest wealth creators of the 20th century were critics of inheritance too, but also put their words into action ("Giving pledges" by Buffett and Gates). So we can see some progress in society even if the death tax hasn't increased.