Talking from experience. I did it to my Mom too. Finally I had some choices, move out or get in line with Mom's rules. (I got an MIP at 18 too. So did both my brothers) It is pretty common. But don't ask for stats. (I have none)
Prior it was a long battle between Mom and my lifestyle. I started out at 15. I never went any farther than beer minus a few horrible experiences with hard liquor. Truth is as a teenager parties are fun. It will screw you up in school, work and life. But it seems like fun. These guys are your friends. "Misery loves company." If a person with an addiction problem that does not want help is a lot like trying to show someone in the WT that there is a problem with what the doctrine does to the individuals perception of reality. (They will not listen until they either hit rock bottom or something happens that changes them.) I doubt your son sees the reality of what drinking does to a person at a young age. It makes them less focused on success. Which is the goal, escapism. The real question is how can he afford it?
When the real world hit me in the face, meaning rent, food, power, forget things like phone and tv. No way, drinking was something I could not afford. And just getting someone to rent me an apartment was such a hassle. Nothing like the real world slapping you in the face to make you pull your head out of your butt. My Mom kicking my bum ass to the curb was the kindist thing she could have done. I thought I knew it all. And with someone else paying the real bills it was all figured out.
The thing to remember is at 18 he is not wearing dipers any more. He is a man. And as a man if he will not respect you then you will have to give him his first lesson in life. If you crap on those who love and care for you at some point they will stop providing you the ability to hurt them. Don't be a door mat not even for your son.
BTW is he still on your auto ins? Because if he hits someone in your car or one on your policy you can be sued. And if he is drunk the policy might not pay out. It happened to my parents with my brother. (He was not drunk or drinking) They were sued for 2 million dollars. And they don't have any money to sue for. (It was settled out of court with the ins.)
Anyway I hope something here is worth using.IMO If it's your house it's your rules.