I've seen this before. A Muslim terrorist slays a non-Muslim citizen in the West, and representatives of the Muslim community rush to dissociate themselves and their faith from the horror. After British soldier Lee Rigby was hacked to death last week in Woolwich in south London, Julie Siddiqi, representing the Islamic Society of Britain, quickly stepped before the microphones to attest that all good Muslims were "sickened" by the attack, "just like everyone else."

This happens every time. Muslim men wearing...