> I think you own your body when you die the same way you own your money: you can specify what should be done with it while you are alive

You have the freedom to specify what exactly should be done with your stuff when you die. Whether those wishes will be legally enforced will depend heavily on what they say.

To test this thesis, go to a lawyer in your jurisdiction and ask them about whether it would be possible to split the proceeds of your estate in equal shares with every man in the Greater London area who wears brown shoes on a Thursday, and prepare for a short explanation of administratively workablity.

Then ask about whether you could posthumously fund some international terrorist organisations. Actually, maybe don't.