Getting a leg up in life because your parents left you a big inheritance, is unfair to those who don't. There are many different types of fairness, not just one.
Are you arguing that no one should be allowed to be a pro basketball player or musician?
You should go read a story called Harrison Bergeron by Kurt Vonnegut.
The way we account for that is is not by outlawing behaviors. Rather, we levy progressive income taxes so that people who are lucky can help people who are less lucky. The most talented basketball players pay a large income tax that helps provide services to those who were not born lucky.
I don't see why estate taxes are any different. It is not fair that some people are born into rich families while others are born into poor families. Nobody is suggesting we outlaw inheritance. But levying an appropriate tax on inheritance and preventing tax avoidance schemes is one way to compensate the unlucky.
Vonnegut was also a socialist (according to Wikipedia).
That would be "fair", yes?
We always tax money when it transfers from one person or entity to another.
Proving my point that the rule is that money is taxed when it changes hands and the exceptions are exceptions.