I agree with Spartydog that the OP’s premise (that the estate tax is not a tax on heirs) is just flat out wrong. There’s nothing wrong with taxing a transfer of money, and as it turns out, for the vast majority of people, the estate tax is a massive tax benefit not burden. Spartydog got part of the way there by pointing out that absent the estate tax we should tax inheritances as income, but that’s not even the biggest aspect of the shelter. That prize goes to the cost basis step-up. Let me explain.
Person A buys $100,000 worth of stock, and sees it appreciate to $3M over the course of his lifetime. If he were to sell that stock and then bequeath the proceeds to his heirs, he would be taxed on $2.9M in capital gains (call it 20%, if A sells after 2011), which is $580K. But suppose instead he just lets his heirs inherit the stock itself. The heirs pay no tax, as the estate is less than $3.5M. Now things get magical: the cost basis of the stock goes up to $3M, so if his heirs immediately turn around and sell the stock, they pay no taxes at all. The entire capital gains of A’s stock have been shielded from tax liability.
What people forget is that the estate tax hits the entire estate, which includes things like unrealized capital gains that have not yet been taxed. Arguing to eliminate the estate tax is arguing to allow huge quantities of money (e.g., the Walton estate, much of which is tied up in stock that represents unrealized capital gains) to be made absolutely tax free. The Walton heirs would never be double taxed on their inheritance; eliminating the estate tax means they won’t be taxed at all.