School Shootings

After the third school shooting in the US in the past week, I'm beginning to think that if I ever have children I'm going to home school them - there is a marginally smaller chance of me killing them than a rampaging gunman.
Today a gunman has gone into an Amish school, separated the girls from the boys, and injured all of the girls in some way, killing at least three of them. Now surely the Amish population would have thought that their very lifestyle would have helped to make them safe from this sort of modern scurge, but alas no. The gunman was not Amish and killed himself, so the reason may not be discovered, although he told his wife just before he shot himself that he was seeking revenge for an event which occurred 20 years ago. He was 32, so he has been holding a grudge since he was 12.
Earlier this week Colorado, who have surely already had thier fair share of school shooting tragedy, were subject to yet another school shooting where the gunman sexually assaulted a group of girls before killing at least one and then himself. Then a 15 year old in Wisconsin took a gun to school and killed his school principal. Fortunately he was subdued and didn't harm anyone else and was taken into custody.
The majority of school shootings involves kids who have been the victim of bullying who, being adolescent and dramatic, decide to kill the perpetrators. Two out of three gunman in these recent shootings have not been students of the schools in question, they have been adults who left high school decades earlier.
This is total speculation, but this is my theory:
These guys are emotionally still in high school. They were rejected when they were in high school originally, and they are so fucked up that they have sought revenge against the type of person they hold responsible for their failings in life.
Wake up sunshine - YOU are responsible for fucking up your life, not the blonde 12 year old who rejected you in 1976. Kill yourself, not children.