Suicide is illegal. Quite frankly the conversation should probably end there, but I'd like to address your points.
The enjoyment you're feeling is caused by nicotine, which is a stimulant. While it is addictive, it's also responsible for the mood-altering effect when one smokes (and to a lesser degree when one uses a patch or gum). I'm sure it feels like a strange combination of wakefulness and relaxation. Unfortunately, this effect, combined with the addictive nature of nicotine, manages to remove the ability to make a sober decision regarding smoking. It's not unlike someone being asked if they should continue drinking when they are already drunk. It is this issue, above all else, that really bothers me. When a person is stripped of their ability to make a sober decision, they are a prisoner. I cannot imagine allowing anyone to be left in such a condition.
I'm glad you posted, morph. Writing this post has helped me to clarify my own stance on this issue.