Suicide is an offence which is the only act of harm done and the perpetrator is never available to be punished or to repent.
The society can tolerate an unpunished criminal, but it cannot tolerate an unrepentant one. Thereby all religions assign hell to the successful suiciders!!
Further the society which glorifies LIFE cannot be seen as recommending something (Death), which itself – by the mere fact of living- is not practicing.
As an extension of this idea, it is unable to take a call on EUTHANASIA also.
Had it been because of HOPE, that the society in a short while wud be able to provide relief to the despondent and retrieve him/her from Death as a relief option, i’d have agreed. But denying someone his wishes, because of the society’s helplessness, is a sin.