Suicide (or its attempt, for that matter) is very rarely prosecuted; I've been a cop in Detroit for 13 years and have never heard of a case going to trial.

While it is illegal, I think the biggest reason that it is is both as a declaration by society that life is sacred (ignore whatever irony you may find in that statement), and as a means for authorities to take action. The "action" taken is usually to force the person to seek psychological treatment.

What the police and EMS usually do on a run to an attempted suicide (or even threats or reasonable belief that a person is suicidal) is take the person to a crisis center (the psychological "emergency room") and have them talk to a shrink. If they don't want to go, we can "petition" them, which is a quicky court order to make them get treatment. The court order is based on our observations, or those of a petitioning party (usually a friend or relative).

Never mind Kervorkian, he was prosecuted because he was just flagrantly rubbing it in the court's faces, over and over.