We don’t require a medical reason to enhance or build our bodies, we don’t need one to damage or destroy them.
I’m already allowed to eat fried foods 10 times a day and chainsmoke and do it slowly and painfully; if that is legal then anyone should be allowed to do it in a quick, painless, and dignified fashion.
Should it be illegal for the doctor to deny me an amputation that I ask for? After all, I should be "free to destroy myself" absent any justification?
Not in a dignified, foolproof way. E.g. can you go to a pharmacy and get a dose of morphine that will kill you with certainty? You can't, in most jurisdictions.
Forcing other people to deal with the trauma of cleaning up your bloody remains after you jump off a window isn't exactly compassionate either.
Give people a clean way out, even if you don't want it for yourself.
I am not sure that we "should be free" to end our life as you say. Sure, we did not have any say about coming to life but I think that if you don't have any incurable disease that causes you significant pain, you can always find something that will make life worthwhile. Unless you are born in Northern Korea or some country that restricts your freedom.