The WHO and many other organisations focus on suicide prevention, and if by this is meant prevention of the causes that lead people to try to end their lives, then this focus is entirely sound. But if by ‘suicide prevention’ is meant simply preventing people from succeeding in killing themselves, irrespective of whether it is possible to change the conditions that lead them to wish to kill themselves, then suicide prevention is not always the right thing to do. It is possible that in a significant number of cases, suicide is the only way of escaping from unbearable and unrelievable suffering due to mental illness, and is in accordance with the rational preferences of the person committing suicide.

(Peter Singer "Voluntary Euthanasia: A Utilitarian Perspective")