Underage Drinking, with the parents permission when did this become the social norm?

While hanging out with Zack and his friend Aj. I asked them what they did this past weekend and to know surprise to me again it was drinking! Now I know that I was no angel in my day but, I do know that I wasn't always drinking every weekend. not at the age of 17. So of course I ask the same questions, where did you drink, where did you get it and why? And while the tow last questions usually differ the question of where did you drink is usually the same. aj's girlfriends house. So usually I just leave it at that and call it a day but, I wanted to know where this mother was at and if she was married. the nosy questions. Aj was a little reluctant but, then said that her mom is single and is constantly going out on dates and doesn't care if they drink just as long as they stay there and then to my amazement he then told me that she usually buys it for them? what? buys it for them, when did this become the social norm? someone tell me when this happened! anyways I am coming to realize that obtaining alcohol is extremely easy at age 17 which is very odd to me and drinking is all these kids want to do on the weekends and it doesn't matter what it is bourbon, maddog, something called 20/20. alcohol I have never heard of but apparently you can get "fuc**d up for 5 dollars by buying this 20/20 concoction. Amazingly enough I assumed that maybe it was just a high school thing and that being in college getting "fuc**d up" wouldn't be the goal for the whole week but boy oh boy was I wrong as I read on Brittany's myspace and pics I believe 130 of them that were all about people getting drunk and passing out with the picture album saying "my weekend". Her and her friends were completely blitzed (drunk) and her fiance was half naked in a lot of them. sure they looked like they had a good time and they all stayed in and didn't leave after they started drinking but, does that make it right? Both brittany and zack are underage and are drinking on the weekends regularly and yes they seem to be "responsible" (and I say that loosely) while they are drinking but, parents neither of them in this case theirs are enabling these children to "act" the part of being adults by providing them alcohol! When did this become the social norm? Does anyone know?