The economic argument in favor of the Federal inheritance tax is that when rich kids born with silver spoons in their mouths inherit millions then all they do is smoke dope and snort coke and travel around the world and they do not do anything productive so they become parasites upon society.... I suggest you watch The Pirates of Silicon Valley for starters and then read the real story. Research though, I'm guessing for you, is not one of your strong suits.
The real reason for the Federal inheritance tax is simply for revenue. It is like the sin taxes -- alcohol excise tax and tobacco excise tax etc.