[stewy]

Many cases of suicide, I would imagine, are committed due to a sense of loss of past pleasures (i.e. after a divorce/bankruptcy, etc.). Committing suicide, then, might be an affirmation of the desirability of past life experience.

I personally would wish non-existence only if my existence caused great harm. For example, if I was responsible for the loss of many lives due to my negligence as, say, a pilot, or a nuclear plant safety officer, I might wish that I had never been born.