The idea is not to get more of the populace taking those - that would be insane - the idea is to medicate people who have an actual depression.
I take sertraline (just 25mg, that is half of the usual starting dosage) to medicate my double depression and so far it has been a great help. For the first time in two decades I feel even-tempered and more or less happy with my life. There are side effects, but it is absolutely worth it.
The SSRIs probably aren't the cause for shootings, the underlying depression, which apparently wasn't successfully treated is far more likely the cause.
Funny fact, I used to own firearms (for target shooting), but sold them years ago. Never had the urge to kill anybody but myself, though.