Joseph, that is a very reasonable response, but it's a non-answer, in my opinion.
Literally everyone has done stupid things to look cool or be accepted by peers, especially in those insecure teenage years. And most people enjoy things that feel good. That's why we like orgasms, sugar, and salt – among other pleasures.
The problem with chemically addictive substances is that a few bad/ignorant decisions, made in those nearly universal pursuits of fitting in or feeling good, can change the chemical makeup of the brain and create a physical dependency. Addiction means you need the substance just to feel normal.
So yes, obviously, self-destructive behavior can be a coping mechanism for pain or helplessness. However, addictive substances like nicotine and opiates are often experimented with by people who have no special emotional pain (beyond the universal human pain you mention), but using the substance creates a hole, i.e., emotional lack, that can only be filled by the substance.
That's why cigarettes, heroin, etc. are so dangerous, and categorizing all addiction as "inner pain" the subject needs to work through is naive, in my opinion. Often the only inner pain is that caused by the addictive substance.
That said, I don't disagree with gesman's general premise for the psychological component of addiction; I just think it's overly broad and dangerously dismissive of the destructive power of addictive drugs.