I don’t see depression as the underlying root cause. I see your “rational suicide” as a means of giving up under the pretense of rationally deciding your own fate. I won’t comment on euthanasia and its implications, because I myself am still formulating an opinion on it. However, if you’re trying to justify rational suicide when it isn’t a case of life and death, then I have to disagree with you. (By which I mean, for example, someone who may be in a dire financial or personal situation from which there is no escape.)
In those cases I see rational suicide as simply giving up pathetically. Why die? When you die, it’s all over. Nothing will be changed when you’re dead. As long as you’re still alive, there is a chance for you to change things, for things to improve. If you give up and die, there will be nothing left. It will be all over. In these cases suicide is merely a cowardly way of escape from your life’s problems. Of course, some people, like the example of Albus Dumbledore that you decided, for political reasons or whatever choose to be a martyr. All the more power to ya, but that’s probably not applicable to most people on this planet.