> to agree to being eaten by a friendly cannibal
They had standards though, you'd have to work to gain the respect for anyone to want to eat you as a mortuary ritual.
1. the right to not have someone else do stuff to your body
2. your right to do anything to it
Number 1 is pretty well established.
Number 2 less so, and I think that comes down to us as a society noticing that many people can't be trusted with full access here. Ask any clean addict and they will tell you what a colossal mistake it was to start using the drug in the first place. The regulation of what you can do with your own body is, in my opinion, a regulation to protect future you from present you. Because we all know what the present you has worse impulse control and judgement than future you would like.
My country is an example where it failed anyway. Whether we are considered to have tried regulating it or not is a bit complicated.