I should emphasize that even if Smith's theory is correct, it in no way justifies the shooters' acts. Killing people is not a defensible response to social putdowns. Her theory also does not change the reality that the overwhelming majority of "stupid nerds" aren't dangerous [my emphasis]. Even if school shooters are more common in this subgroup than in others, they would still be only a miniscule fraction of the total "stupid nerd" population.
As Somin points out--school shooters are rare--most kids, nerds or not, never act out in this violent way. I was simply talking about out of the ones who do. Part of the problem with pinpointing the psychological traits of school shooters is that luckily, there are so very few.