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Yes, there are potentially legal issues involved with selling the addresses. It is, essentially, participating in sending unsolicited email, which is called spam, for which there are increasingly tougher laws, and severer penalties.
Some of the unsolicited mail could involve fraud, and since you are targeting families of teenagers, think of the ramifications of selling addresses, and having spam mail for skin flicks being sent to 13 year old boys - and then the parents find out you were the one who made the email address available? They've gotcha, and they are not gonna be happy.
The only advice that can be given to you is to check with a qualified attorney or the appropriate law enforcement agency to verify whether or not this would be potentially raising legal or liability issues for you. Due to the questionable nature of this, I don't think any of us can really advise you any further than the wisdom of making sure you protect your interests.
Let me start off by saying I hate spam too!:) However, I think you would have a hard time making a case of selling customer data criminal. If you ever read any of the privacy policies of some of the dot bombs Justin mentioned, I can just about guarantee that there was the standard clause in them that the "may from time to time share the data."
When a dot com goes out of business, their client list is probably the most valuable assest they have. If they go bankrupt, and close shop owing money to creditors, The court will force them to sell anything of value to pay their debts. It happens all the time.