[Melusine]

That's absolutely not true. A severe clinical depression, while treatable, is not something that will 'just pick up'.
However, in most cases of teen angst it WOULD be a waste... almost everybody at some point in their life wonders what's the use of it all.
So mostly I agree with Neb: it should be allowed, but we do have an obligation to help people and prevent them from killing themselves, as in most cases, things WILL get better.
Still, in the end I think it's a person's right to decide about their own life and death (not going into dodgy territory like criminals on hunger strike etc here, just generally speaking)
So we should do all we can to prevent it, yet respect a person's wishes if there's really nothing left for them to care about in the world.