What is it about "celebrating" in a group that causes people to lose all sense of law and order - not all people of course. That's what makes it so fascinating that some destroy property for the sheer experience of doing it while most people would be appalled at the idea. San Francisco police have been circulating a photo of a post-World Series Championship "reveler" smashing the windshield of a $1M city bus that was later set ablaze, hoping that he will be identified.
When social norms work in conjunction with law, they assist the process of maintaining order. For instance, there is no need for a law that requires everyone to wear their underwear on the inside of their clothes. Since that is the social norm, instances of folks wearing their underwear on the outside of their clothes are pretty rare. However, when the norm of a rogue group runs counter to the law, there is a problem. Just because your conduct may be acceptable to a growing band of miscreants at a particular place and time, doesn't meant that it is acceptable to society at large. You and your buddies may regularly urinate on the lawns of the people who live near campus on your drunken walks back to your student apartment. That doesn't make it acceptable.
See related post here.
The San Francisco bus smashing reveler