No matter how many values a parent instills in their teen. they will still act the way they want. If a teen is going through a rebellious stage and takes up gambling it usually doesn't have anything to do with what their parents taught them.
@SjOnFire, this is a very subjective topic, that no one ought to generalize. Not all teens will act the way they want. I was raised with very strict parents who told you what was right, but never tried too much to stop from doing these 'bad' things. I remember very many instances where I made a fool of myself, and learned the hard way.
The point here is not people giving up gambling completely, but starting it after your teens because this is the age where we like to experiment and without proper mentorship, we could end up being miserable. If I may ask, when did you start gambling? Secondly, would you let your children participate in gambling in their teens, without caring to tell them the risks involved? Would you always give money without asking them to account for it?
All in all, and like
@zephyr 12 says, I agree that gambling has demonized for a long time and that analogy to alcohol, brings out the harsh reality. The truth of the matter is that irresponsible and responsible gambling are two sides of the same coin, whichever way we choose to look at it.