In the 70's we used to laugh about saying "high school" because there were so many drugs floating around at school. Guess what, we had no school shooters and the most you could get from the school nurse was an asprin.
You have kids smoking pot at 9 and 10 years now. And it's not the pot that existed 20 or 30 years ago. This is hybrid stuff. You also have teens taking drugs that contain weird psychotropic cocktails.
What we now have is a situation where kids are getting dosed with odd concoctions from before they are born...does this make for school shooters? Maybe. And when you say that you didn't have kids shooting up the school, I'll bet your school -- like the vast majority -- had a couple kids who showed sociopathic behavior, such as killing small animals or random acts of viciousness.