The perpetrators at least have something resembling an excuse. Although specific medical diagnoses of any given mass shooter fall along a spectrum that may or may not include the frequent, often wrongly used catch-all term, “psychopath,” I strongly doubt that any mental health professional would disagree that all such perpetrators are, by both common and professional understanding, “disordered.” Whatever compulsions inspire them to commit such heinous acts, it sets them at odds, in a profoundly anti-social way, from most all the rest of their societal peers who reflexively recoil from what they have beheld. I don’t pretend to understand the precise…