It’s not about regulation it’s about intervention. It’s not that you’re not allowed to saw pieces of yourself off with a chainsaw, stranger of a choice as that may be. The idea is people in your life who care about you may want to intervene to stop you, as no matter how pleasurable you might find what you’re doing to be, it’s slowly killing you.
And that’s not even going into the science behind addiction where the whole “but you chose to do this” gets more and more dubious the deeper you go.