It is ridiculous that people want to involve doctors when they can do it themselves.
The same rational exists for legalizing suicide. If you want to kill yourself, you can, and thus also avoid punishment from society.
There is NO GOOD reason to legalize either suicide or doctor assisted suicide.
Another point is that yet again, people don't want to take responsibility for their own lives and actions. Suicide has a social stigma attached to it (as well it should) and has throughout history. This way people can take "doctor prescribed medication" to commit suicide and every feels all warm and fuzzy about it.
And the next scene is "Gosh, Grandma, don't you know that Auntie Pheobe took the medicine the doctor prescribed and now she has no pain? And look how much it costs to keep you alive now that you can't feed or dress yourself..."