Suicide in Middle Earth

[Elenhin]

I agree with Kuruharan and Mat Heathertoes: the deaths of the Numenorean kings can't be called suicides. The lived to the ends of their natural lifespans and then died by their own free wills. The later kings of Numenor, on the other hand, tried to live longer than it was natural. Of the first Numenorean king to do so, Tolkien says the following: "And Atanamir lived to a great age, clinging to his life beyond the end of all joy... refusing to depart until he was witless and unmanned...". Remember also that in Numenor "wise men laboured unceasingly to discover if they might the secret of recalling life, or at the least of prolonging of Men's days". This doesn't sound very natural to me.
Of course, same kind of things could be said about modern medicine... andperhaps Tolkien is trying to.

I think that Elves who die to depression are very different from despaired Men who commit suicide. Elves go to Mandos for healing and may return to life, but a Man's lifetime in Arda is limited. A Man should use his life for good purposes and not to abandon it without purpose. If an Elf dies to depression... well, it wasn't his own choice to be so depressed and if there was any other way out, I'm sure that no Elf would have to resort to abandoning his body. A Man who commits suicide in desperation is not looking for healing or solution to the situation at hand, but escape from it. Denethor could have, for example, died honorably like Theoden and fulfilled his obligation to his people.