It started, i believe, because a kid was either arrested or killed (being in th uk, I'm guessing arrested). in my opinion that isn't enough to justify that behavior...even if it was wrong. However, I think most of the kids (and, much like the hippies of the 60's, not ALL were underclass) were using it as a reason to loot and misbehave. A few of them may have been outraged, but what good is rioting? All that does is make your cause get lost in the destruction and your behavior widely criticised. It doesn't change anything.
I remember the LA riots. I don't live anywhere near there, but I think it was racial issues. Was it the Rodney King beating? I remember that many of the shop owners defended their own stores/property with guns. It seemed very surreal to me as I have never experienced anything like that and probably won't since we live in a small town where there is basically almost no crime.
On the Pensylvania story, In Philadelphia I guess the gangs are getting wild and running around all night and probably causing danger to themselves and others so the city inplemented a curfew. Most of our drama is in the big cities.
I love the peace and quiet of more rural areas. Even the Madison Wisconsin demonstrations for the teacher's unions got on my nerves because a lot of the protesters were not behaving well and were destroying property (I believe it hurt their cause rather than helped it in Wisconsin). If any teacher had taken my kid to protest without my permission....grrrrrrrrrr...they would not have been happy.
I am just more of a peaceful person, not moved by bad behavior. I don't really care what triggered it. Innocent people and their property should not be destroyed just because somebody is angry. I never understood that reasoning. We see this all too often in many parts of the world....and in the past it has happened here too.