The Last Ditch has a very good comment piece on Teenage Drinking.
I'd add two further comments.
1..Before drinking was permitted all day in 1987ish (previously pubs had to close 3pm-7pm), similar dire predictions about increases in drink-related violence during the day were raised. Not only did they fail to materialise, disorder actually dropped, as those who wished to drink all day were no longer forced out onto the streets. This had been a real problem in my town, and it practically vanished overnight.
2..Even if things do get temporarily worse, we have to change the culture. A foreign commentator, it may have been PJ O'Rourke, once observed that while the Americans drink to relax and enjoy themselves, and the Europeans to be sociable, the British drink like someone's going to take it away from them. That's because they do ! It's unrealistic to expect us to adopt a cafe culture overnight, but perhaps over time people will no longer feel compelled to to pour as much beer down their necks as possible before eleven o'clock.