I expect everyone here to disagree with me completely. That's fine.
"School shooters" are evil losers. Without exception. I don't care why they do it. I don't care if they claim they were bullied. I have no sympathy whatsoever. Especially when they use the bullying as their excuse to shoot people who weren't the ones bullying them.
However, if they target only those who are bullying them, I also have zero sympathy for their "victims". Bullies are evil losers, too. I don't care even a little about what happens to them.
Sometimes bad guys clash with bad guys and bad guys die. Ho hum.
Bullying has a price, but it is one that is rarely paid. That doesn't mean it is never paid.
Bullying is not that much different than murder, and bullying can include murder. Murderers are bullies. Murder is when the bullying becomes final. Bullying can be murder that takes decades to kill, or it can kill through suicide a lot faster. I'm in favor of bullies being stopped in the act, however that is accomplished. And I'll never care about them.