Wow so on one side of the planet a group of people kills one person in a school for having a different opinion while on the other side a person kills a group of people in a school also for having a different opinion. In all cases it's because of disagreements, and in all cases they are extremists. To me it's all about education.
It doesn't matter if you are religious or not if you are an extremist you will do extreme actions and sometimes it will end up into killings. Extremists are the ones that needs to be taught a lesson and education needs to come first.