I don't know if you remember, but back "in the day" I wrote a series of horror stories called "Random acts of Violence" - it has been an idea I have had since a kid essentially. But of course, nothing is random, right? 

All of these things have a long line of catalysts to push people to the point that they break and coupled with the variance in personalities and abilities for self control etc, it is bound to happen. It is an economic reaction, where incentives align to drive a trend and set of a actions and reactions. 

Nothing to live for or trapped in the corner, when it is happening to tens of millions of people globally at the same time, there is going to be a percentage who will take the next step, which will make that step smaller for those just behind to follow.