Stephen Bryen is actually correct. Carry in church is not the be all end all of making it safe. As he says in his last sentence-- And guns inside holy places by themselves are not a guarantee of security. It is widely recognized as a major deterrent and substantial factor in casualty reduction efforts.
Cameras, watching closely and armed guards were not sufficient to prevent that church shooting. All are factors, all are good steps, none are by themselves enough. The only thing good enough for that is to lock the door and everyone stay home.
Nemo