Having rich parents counts as equal opportunity?
If you put a 100% estate tax, then you're preventing people from working towards one of the biggest goals they work for, i.e. their kids.
Also, if a parent doesn't wanna give his wealth to his kids, no court in America would force the estate to go to the kids.
In other words, nobody is born rich, it's the rich individuals who make their kids rich.
The wealthy individuals are choosing to spend their money as they please. That happens to be by making wealthy some non-wealthy individuals.
In the case of this argument it's parents/children, but it doesn't have to be. The parents choose of their own free will. And they can choose to spend the money instead. Many do. Most, probably.
As I mentioned, the expiring bill would increase consumption but it would also be "wasteful". Someone unable to leave a business to a son might be tempted to build a huge gold statue in the middle of nowhere. Luxury goods would become a much more tempting market, even though the experiences they provide are of very limited value to society as a whole.
Also, figure all the big companies that couldnt exist because there is no legacy, every business owner would sell his business in life and frivolously spend all that money.
That is, if you were able to prevent people effectively from leaving money to their kids, which I assure you, its impossible.
Contrary to how people believe, you can't really 'hoard' money, when you hoard money, you merely invest in money itself, and like every investment, it gives society huge benefits (including, and especially the investor).