Well, it seems there are two things a man cannot resist, the lure of the One Ring and the lure of a good discussion in the Barrow Downs. A hearty hello for those of you who remember me! And another hello for those of you who will be hearing from me for the first time.
Talking about suicide in Middle Earth, and even though this has already been stated to a higher or lesser degree, I find there are two kinds of "self-inflicted deaths"
On one hand we have the relenquishing of life by the Kings of Numenor, which I've always thought was less of a suicide/self inflicted death and more of an acknowledgement that his time had come as ordained by Iluvatar (and thus, not really the King's fault). It was
not borne out of despair or any other selfish feelings and perhaps it was not even a real choice for the king. It might have been a sudden insight that the time had come and that Illuvatar wished him to pass on to whatever fate men had. What man not swayed by the shadows would refuse Iluvatar's will? Thus it is not much of a choice, is it?
On the other hand we have the taking of one's life by violence, like Turin did when he took a dive on Mormegil. While one can say that his motives were altrusitic because all he had done had come to grief and thus by removing himself from Arda he would avoid bringing
further trouble to his loved ones, it was a selfish act and quite likely against the will of Iluvatar. After all, if I know my christian theology properly, it is said that G'd has a plan for each of us and that no matter how tough things might look He knows what He is doing and in the end it all becomes clear. So assuming Tolkien borrowed from this tradition, by killing himself, Turin might've not only acted against Iluvatar's will but he might have also prevented Iluvatar's plan for him from being fulfilled. Perhaps Turin, after all his failures, would have in the end won a redeeming battle against Morgoth. We will never know.
Then there are other scenarios that have been brought up. Hurin's "last stand" is an example of, essentially, giving up on life (even if for a very altruistic cause). However, how does this fit in with Iluvatar's "plan"? Well, since Hurin did not slay himself and instead he fought hard and well against those who would slay him, it is clear
he was not making the choice. If it was Iluvatar's will that he would die so others could live he was willing to make that sacrifice, but as we see that is not what happens. So Hurin is not making a choice that is not his to make (that is, WHEN to die) but rather making a choice that is very much within his responsability as a leader of men in war.
Finally there is the example of the elves which I find is no death at all (although that's not to say that there is no fault in it). If we part from the premises that
a) Elves do not really die the same way men do
b) The Halls of Mandos is a place of healing and restoring, and
c) The elves know this
then I hope we can agree there is no fault in allowing their fea to leave their hroa if they feel overwhelmed by Arda Marred. We must understand that elves (or at least elves in Middle Earth) are constantly faced with matters they were not "meant to". They were meant to be in Arda Unmarred and to take energy from Arda itself. Since they instead take their energy from Arda
Marred, they will at times be caught in situations to which they are unable to find a way out. That's where the Halls of Mandos comes in, I have been slowly making my way through HoME and I just read "Laws and customs of the elves" (I think that's the name) and it changed my perspective on Mandos
I used to think Mandos was a place of punishment, and it may be after a fashion, but it is also a place of healing, where the discrepancies between what elves SHOULD have experienced (Arda Unmarred) and what they DO experience (Arda Marred) are reconciled so that the elf (if both him and Mandos so choose) can return to physical life.
So, while not exactly ideal or natural, the elves do not
die as men do, and their (potentially temporary) lack of physical life does not mean an end to their spirit's life in Middle Earth. Conversely, for men there might be another kind of life, but it is beyond Middle Earth.
Unfortunately I've run out of time so I do not know if I'm making sense or not but must leave in a hurry
. I will try to come back and edit this post later on tonight if I get the chance, but I hope what I wrote makes as much sense here as it did in my head!