Its not broke, what is there to fix? Oh, wait, the unfixable - the PARENTS.
Just assuming for a second that this isn't a troll, insulting the people who have the ultimate power in this situation isn't going to convince anybody.
As for the pot smoking, and the alcohol, that's about as dangerous as watching ghost rider. Alright bad example, that movie sucked ass. But the point remains that trying to control your children is only going to lead to more division and resistance. At 17 most people are tired of
waiting to become someone. So they don't.
Having a separate identity doesn't malign any intentions that you have upon them, unless it's to overpower who they are because you want them to be someone else. In the end, all you can really do is guide them; point out the consequences of their actions; and hope they make the best decision. If you believe whole-heartedly in your convictions, explaining them to others is the only true way to convince someone.
In short, work on your communication.