Coldits, when I was 18, I had already been using public transport on my own for 8 years, I had a driving license (for when my younger sister needed a lift), I could cook my own meals, ensure I didn't get myself in trouble and found it stupid to get drunk (I found it cool and hilarious at 14 though).
I don't remember asking my parents "to let me go to..." anywhere, I just took my own decisions and my parents respected them as long as they knew at what time they should ring the police I was coming back.
I was getting a small quantity of money a week while I was at University, such a princely sum... I needed to save for 3 days to be able to afford a jacket potato. If I needed more money, I needed to earn it myself.
I suppose that 20 years ago, parents ensured their offspring had been gradually turned independent and their own persons by the time they turned 18. Nowadays I get shocked to see parents of 20+ years old organising everything and bailing them out of whatever in the way my parents did when I was 12.
Obviously, if the child has not been allowed to become a responsible individual (either by upbringing or because that's the way things are in society nowadays), is still fully dependent on his parents to provide for all his needs, it is only fair for the parent to set some rules in her own house. If the son wants to be treated like an adult he needs to behave like one, until then, he is just a drunk spoiled child taking advantage of the good will of the parents.
I also have a "child of divorced parents" and I often find it difficult to do what I am supposed to do because he has/ is having such a bad time. I cut him some slack, he has not had an easy life, but when it comes to discipline, I often ask myself the question "Would I allow him to behave like that if we were still married?" The answer is normally... the right one.