The absolute first thing taught at infantry basic training during the Cold War was that the maximum effective range of an excuse is zero. On the face of it I saw this as the response to any attempt to explain a failure to learn a necessary skill. But this idea also applies to the moral nightmare we were facing during with the Communists enemy and their excuses for their crimes.
Today we are facing another and older nightmare with the onslaught of Islam.
There has been another jihad incident.
The functions of ideologies are first to erase the responsibility of the perpetrators for theirs actions and to deny the humanity of the victims. But there is never a valid excuse for murder.