I see many good points posted here, but let's not get into religion. Religion is not responsible for your actions, nor do you need religion to be a decent person.
I do believe that the celebrity status of mass murderers and serial killers is a big causal factor for the individuals that commit these crimes. However, we must set a side those killings that have been motivated by revenge; when going trough the list of school shootings in the U.S. I found that the majority was revenge motivated, perpetrated by a single student who committed suicide or murder-suicide at his school, usually with very few casualties, often only the perpetrator himself. These kinds of suicide/murder-suicides happen everywhere, and the only reason they are "shootings" in the U.S. is the availability of firearms; especially handguns. In Europe and elsewhere other weapons are used instead, often with much the same result.
The crimes I believe the media and our own celebrity worshiping culture is driving is the lone outsider, often middle-age male who sees himself as a failure, who, as someone put it: wants to "go out with a bang"; to put his mark on the world in the only way he seems able.