I think suicide is for poor people who can't afford euthanasia. I'm not really against it though. We were born involuntarily and I guess if people have the right to live, then logically, they should have the right to die.
Also, I think that discouraging suicide is really selfish in society's part as well. I know it's weird that a whole society could be 'selfish' but that's only because English doesn't have the right word to describe it. The closest word could be 'tyranny' but that's not quite right. I guess, I'd coin the word 'society-ish' for this purpose which means 'only concerned with society's interest whilst ignoring human emotions'.
Alright, so suicide... You know when you think about it, why does society discourage suicide? Is it weird that if a guy kills himself, it is an outcry but when a country declares war, everything is allowed? Well, there's a correlation between them of course. It's simple, dead people don't fight wars and in a war everybody is precious, even if it is just for cannon fodder.
I'd guess that's the first reason why suicide is discouraged. Why slit your own throat when the enemy can do it for you later? I'd guess banning suicide by condemning people to hell was really effective in keeping manpower as high as possible during the Middle Ages.
Of course then you have societies like Japan, which encourages suicide in the face of defeat or dishonor. For Japan, I think it's because it's small and more people=more mouths to feed which is unlike Europe and Asia where countries had room to expand. Also, the wars the Japanese fought was between themselves anyway so whoever wins, it's gotta be a Japanese, from the Japanese society, which means cannon fodder isn't really as required to safeguard the society.
But today, we live not in the World where wars are less important than money. Since money can be obtained by everyone, everywhere; society is now pressured to keep even the most disabled people alive as long as possible.
There are some societies that still holds some values leftover from the warring days; where they kill people who kill their people. But even these societies have begun to start being pressured by everyone to stop doing that.
All of this means that the reason suicide is the devil is really less about religion and more about pragmatism. Society doesn't give a damn whether you go to heaven or hell. What society is concerned about, is that you keep your body functioning as long as possible. So when society needs you to grab society a glass of water or order society a pizza, you won't be a dead piece of meat who can't do any of those stuff.