[Mat_Heathertoes]

I agree with KuruHaran on this. In Tolkiens works there is a marked difference between forcibly trying to take ones life and the relinquishing of it voluntarily as part of the Gift of Men. There are some interesting quotes in the Akallabeth which illustrate how Tolkien perceives mortality in his sub-creative world.

Then the Messengers said: 'Indeed the mind of Illuvatar concerning you is not known to the Valar, and he has not revealed all things that are to come. But this we hold to be true, that your home is not here, neither in the Land of Aman nor anywhere else within the Circles of the World. And the Doom of Men, that they should depart, was at first a gift of Illuvatar. It became a grief to them only because coming under the shadow of Morgoth it seemed to them that they were surrounded by a great darkness, of which they were afraid; and some grew wilful and proud and would not yield, until life was reft from them. We who bear the ever-mounting burden of the years do not clearly understand this; but if that grief has returned to trouble you, as you say, then we fear that the Shadow arises once more and grows again in your hearts. Therefore, though you be Dúnedain, fairest of Men, who escaped from the Shadow of old and fought valiantly against it, we say to you: Beware!

Now this is a very indicative passage by J.R.R. Tolkien and it is expanding upon by other references to the mysterious "fall" of mankind in the East of Middle-Earth before the three Houses of the Edain passed over the Ered Luin in the First Age of Middle-Earth. It appears that by the above quote, the ability to relinquish ones life was part of the original gift of men, as the Valaquenta touches upon ..

'But to the Atani I will give a new gift.' Therefore he [Illuvatar] willed that the hearts of Men should seek beyond the world and should find no rest therein; but they should have a virtue to shape their life; amid the powers and chances of the world, beyond the Music of the Ainur, which is as fate to all things else....

Silmarillion - Chapter 1 - Of The Beginning of Days

So I would argue that Melkor, being the truest to his purpose amongst the Valar, saw his chance, as he tried with the Quendi in the Ages of the Trees and left Angband to go East and corrupt Men in the infancy of their existence

The Valar sat now behind their mountains at peace; and having given light to Middle-Earth they left it for long untended and the lordship of Morgoth was uncontested ....

Silmarillion Chapter 12 'Of Men'

and also ..

But it was said afterwards among the Eldar that when Men awoke in Hildórien at the rising of the Sun spies of Morgoth were watchful, and tidings were soon brought to him; and this seemed to him so great a matter that secretly under shadow he himself departed from Angband, and went forth into Middle-Earth, leaving to Sauron the command of the War. Of his dealings with Men the Eldar indeed knew nothing, at that time, and learnt but little afterwards; but that a darkness lay upon the hearts of Men (as the shadow of the Kinslaying and the Doom of Mandos lay upon the Noldor) they perceived clearly even in the people of the Elf-Friends whom they first knew. To corrupt or destroy whatsoever arose new and fair was ever the chief desire of Morgoth; and doubtless he had his purpose also in his errand: by fear and lies to make Men the foes of the Eldar....

Silmarillion - Chapter 17 - Of the Coming of Men into the West

It was indeed evident that Morgoth had planted lies into the hearts of the fathers of the fathers of the fathers of mankind before they even met the Avari and that these lies were the beginning of the Shadow and the fear of death that all mankind had ...

All this is but Elvish lore. tales to beguile newcomers that are unwary. The Sea has no shore. There is no Light in the West. You have followed the fool-fire of the Elves to the end of the world!

The Silmarillion - Chapter 17 - Of the coming of Men into the West

This last then I will say to you, thrall Morgoth,' said Húrin, 'and it comes not from the lore of the Eldar, but is put into my heart in this hour. You are not the Lord of Men, and shall not be, though all the Arda and Menel fall in your dominion. Beyond the Circles of the World you shall not pursue those who refuse you.'
'Beyond the Circles of the World I will not pursue them,' said Morgoth. 'For beyond the Circles of the World there is Nothing. But within them they shall not escape me, until they enter into Nothing.'
'You lie,' said Húrin.

Narn I Hin Hurin - Unfinished Tales

So as you see, the original 'Fall of Mankind' was the lie, created by Melkor that there was nothing beyond mortal death and that the Eldar did not die and were therefore in some fashion, privileged and to be envied

And Sauron in Numenor echoed this lie as he said to Ar-Pharazon the Golden when, in his pride, he felt old age approach ..

The Valar have possessed themselves of the land where there is no death; and they lie to you concerning it, hiding it as best they may, because of their avarice and their fear is lest the Kings of Men should wrest from them the deathless realm and rule the world in their stead. And though, doubtless, the gift of life unending is not for all, but only for such as are worthy, being men of might and pride and great lineage, yet against all, justice is done that this gift, which is his due, should be withheld from the King of Kings, Ar Pharazon......

Akallabeth

And down the ages this lie seems to be repeated and expanded and sown deeper into the hearts of men, comparable with our own 'Original Sin' in so far, like the men of Tolkiens mythology, the gift of our existence has been spurned and we reap the consequences thereof.

Faramir makes another evocative reference to the passing of the truth and the waning of the Men of the West when he says

'For so we reckon Men in our lore, calling them High, or Men of the West, which were Númenoreans; and the Middle Peoples, Men of the Twilight, such as are the Rohirrim and their kin that dwell still far in the North; and the Wild, the Men of Darkness.'
'Yet now, if the Rohirrim are grown in some ways more like to us, enhanced in arts and gentleness, we too are have become more like to them, and can scare claim any longer the title High....'

But I think JRRT sums it all up neatly when he says ...

But the view of the myth is that Death - the mere shortness of human life-span - is not a punishment for the Fall but a biologically (and therefore also spiritually, since body and spirit are integrated) inherent part of Man's nature. The attempt to escape it is wicked because 'unnatural', and silly because Death in that sense is the Gift of God (envied by the Elves), release from the weariness of Time, Death in the penal sense, is viewed as a change in attitude to it; fear, reluctance. A good Numenorean died of free will when he felt it to be time to do so.

So to sum up it is evident that suicide in the sense of terminating ones existence in a 'forced' sense, i.e self-immolation or by the blade of one's own sword is different from Tolkiens innate, consistent mythological scenario of a "free" [from Shadow] man willfully and peacefully relinquishing his existence within the Circles of the World when he thought it appropriate.

In sorrow we must go, but not in despair. Behold! we are not bound for ever to the circles of the world, and beyond them is more than memory. Farewell!