that’s not how that works, we cant regrow (most) vital organs (liver says hi) because of “engineering problems” not because evolution is random. we personify adaptations to understand them, it can lead to issues but yours is a massive overcorrection.
i feel you are confused. internal review boards, of which there are many, regularly allow human trials. they are necessary for the fda’s approval as well. there are tons of ways for patients to access ethically reviewed experimental treatments, but terminal patients are extremely likely to. you are correct that experimenting on onesself is often far less troubling though