I think whether people have a right to do it (which I also believe they do), is less important than realizing that their desire and decision to do it is based on faulty logic. Depression completely changes the way people think.
But that's the point, right? Depression causes so much pain that some people decide it is better to end their life rather than suffer. I don't see how it's any different than someone in chronic pain from any terminal illness desiring physician-assisted suicide. Of course their decision is affected by the pain they're suffering. That's the whole point.