Good question, why can't Warren Buffet marry his daughter, son, dog?
If it is his son or daughter, and then becomes his spouse, the tax laws are circumvented, because they remain his son or daughter.
If you are worried about a guy marrying his dog, why?
Can the dog express "informed consent?"
If not, then there could be no marriage, as it take informed consent on both parties to enforce a contract, and marriage is a contract.
The issue comes down to where that contract is with the state, or with God, or combined.
Take religion out of it, then it just becomes a contract, and then you have no reason to prevent any person or persons from getting married as long as all parties are capable of informed consent.
One guy has a hundred wives, so what? Some woman has hundred husbands? So what?
These are abnormalities, not anything that is going to happen broadly.
The Saudi king has lots of wives, does that mean that the average citizen of Saudi Arabia has lots of wives? No, they can't afford it.
Quote from Mercor:
With no child in mind the law forbidding relatives to marry is invalid.
Why can't Warren Buffet "marry" his daughter / son / dog / all and have his estate move to the next generation shielded from the Goverment.