The Orlando massacre is a hideous reminder to Americans that homophobia is an integral part of Islamic extremism. That isn’t to say that some people of other faiths and ideologies aren’t hostile to members of the lesbian, gay, bisexual and transgender, or LGBT, community. Nor is to say that Islamic extremists don’t target other minorities, in addition to engaging in wholly indiscriminate violence. But it is important to establish why a man like Omar Mateen could be motivated to murder 49 people in a gay nightclub, interrupting the slaughter, as law-enforcement officials reported, to dial 911, proclaim his support for...