I dont think it's a new phenomena, at all.
I just think it's more easily publicized, and weapons are more powerful.
It's not the media, it's not the "decline of the family unit." If those things were true, it wouldn't be so scarce of an issue. You have to keep things in perspective and not blow them out of proportion. There are 300 M give or take people in just this Country alone. This is not a widespread issue by any stretch of the imagination. But, violence in games and movies, the trend away from Religion and the divorce rates are pretty widespread. There's no necessary correlation.
A better assumption is that some kids are born with a defective brain, some kids are born into horrible home-life situations and can't handle it, and some kids become psychotic due to drugs.
I do agree with a lot of what you say. But couldn't a kid born with a defective brain respond to one or several of points you posted to the point of an outburst?
I do think that not having two parents does create a problem with well adjusted children....take that to a "problem child", it could become a real issue. If a child isn't exposed to children growing up and not bonding, but instead his time is consumed on the internet in a make believe world may not create an issue with normal children, but could have impact on a problem child. IMO, I think religion is important....but that is just me.
I do believe the drugs give to children for ADD and anti depressent drugs might play a huge problem. I saw that first hand with a relatively normal child of a friend of mine. He lashed out with anger and there were suicide issues......Dr. told him that it was a side effect of the drug he took.