HOW do you tell a wealthy heiress from a family farmer? It sounds like the setup for a joke. But in fact it is the fundamental problem underlying sensible reform of the federal estate tax. Members of Congress are hoping to revise the current law on the estate tax by the end of this year; if they don’t, the estate tax will disappear for a year. Lawmakers should use the opportunity to solve the farmer/heiress riddle once and for all and move our tax system closer to the values on which the country was founded — that hard work should...