Utilitarianism is retarded, ergo, all arguments stemming from utilitarian calculus are invalid.
Having said that, I concede that value of life may have some relevance to the issue of suicide. So, here goes:
1. A person in a given moment has rights equal to those of other instances of this person in time, i.e. himself at other moments.
2. Sometimes even very unhappy people strongly prefer to exist, not in the sense that they fear death but rather that they consider life worthwhile.
3. Killing yourself when unhappy automatically kills those happy instances by precluding their existence.
4. It is immoral to kill people who have a preference to exist. It is, however, not immoral to deny people death when they don't have such preference.
> Why would you like to experience a shitty time?
This isn't a kino, degenerate.