The details are different, but the story is the same: A killer with access to military-style weaponry mows down innocent Americans in cold blood. On Sunday it was apparently a self-radicalized Muslim who murdered 49 patrons of a gay nightclub in Orlando. In 2012, it was a mentally ill man with the same type of gun who killed 26 at an elementary school in Newtown, Conn. Next, who knows? It makes no more sense to blame Islam for the Orlando shooting than it would to blame mental illness for the Sandy Hook massacre. The common thread and decisive factor in...