So why do these shootings happen so often in the United States?

[bedstuy]

I'm sure it's a complicated, multivariate answer.

But, I wonder whether the United States and the first world in general is seeing a sort of epidemic in congenital mental illness.  Schizophrenia and autism have been tied recently to the age of the father.  Perhaps, the trend towards older parents is leading to greater numbers of people with a genetic predisposition towards this sort of activity.