First off, there is no such thing as a death tax.  When you die you can't take it with you or be taxed on it.  Even the IRS can't hunt you down, or up once you die.

Its an income tax on the inheritors of the estate. 

Because "someone in their family earned" the money doesn't mean that the next guy in the chain's income shouldn't be taxable. 

What you do get is a HUGE tax break on your income from the estate.  What other income lets you have over five million dollars before you owe any tax?

The lottery tax is higher than that and I pay the state for the lottery ticket to start with and split the pot with them!

If I make $100,000 by working hard, I pay more taxes than you pay on $5,000,000 income that you get through an accident of birth and a kind parent.