>Inheritance is extremely unmeritocratic yet is somehow completely acceptable even among hardcore libertarians. Why?
I think you grossly misinterpret the philosophy of serious libertarians. It's not simply about meritocracy, it's much more about being free to control what's lawfully yours such as personal and business assets (including your body and voluntary economic agency). This of course includes having the right to decide who gets your money after you die.
>it leads to a less efficient use of resources. We have all of history to tell us it's a bad idea.
Do we really? Inheritance taxes are a minority of government revenues, and they fall well into being offset by the sheer waste of resources and money that most governments routinely practice. You consider them being handed down into often useful foundations worse than this?
>People who inherit their wealth have no such justification. Let wealth die with the person.
How about letting the people who created their wealth decide what's a fair use of it? They're in a practical sense more justified than anyone else in having that decision. You or some bureucrat are somehow more justified than the creator of a body of wealth in deciding what should happen with it? How so pray tell?