Many of these people are outcasts of some sort who feel they have nothing to lose anymore, calling them insane is just an easy explanation for people who don't want to think about it or reconsider anything.
Then again if you think it's normal, why are you so shocked and sad? If you're saying it's essentially no different from the 500 traffic deaths every year then there's no reason to be any more sorry over this than over the 500 dead people from traffic accidents every year.