Governments can be predators and they can be incompetent. They are often both. Going to war unleashes multiple horrors, including the expansion of government's role and reach. This is why libertarians and others insist that going to war is a last resort, reserved for genuine emergencies.
The current debate is over the question of whether we are now in one of these. That sentiment will change when the next outrage occurs. Given how easy these are to perpetrate, what are the odds? No one knows but we now know how easy they are to mount. No one needs to learn to fly a jetliner.
The London subway attacks emboldened security forces as well as the many plotters. I fear that they were most inspiring to the psychopaths. 7/7 may turn out to be more ominous than 9/11.