Actually, most of the shooters did not have any "raising by fathers." While I can be proven wrong, most came from broken families and/or terrible male figures. This doesn't have to do with this "not how discuss emotion nonsense." You didn't have a bunch of school shootings in the early 1900s when men stoic masculinity was at is highest. A generation suffered under two World Worlds, and didn't come home and shoot up schools or even raise kids that did. (Other issues, sure, but we are talking about school shootings here).
Everyone on this thread so far is only offering pop culture bullshit pontifications of truly what is ailing these sad individuals. Very little has been offered so far that these shootings have been somehow a product of emasculations. While obviously these offenders have been men. One cannot draw the conclusion that it is "masculinity" in general that is the issue.
Moreover, (and off topic), this whole notion of "toxic masculinity" is IMO more trouble than its worth because as the we have sought to redefine what femininity is (and all for the best), society has yet to redefine masculinity, and what that means beyond the jokes of the beer drinking, kinda chunky, sports fan.