the Ultimate Goal is to create and maintain as much of an ideal society as we can pragmatically attain. An ideal society has no crime. In Canada we've realized we can't entirely eliminate crime, because many of the more drastic measures to "get tough on crime" have harmful side-effects that take us further away from the ideal society, not closer towards it.
We take the same arguments towards cigarettes, alcohol, automobile speeding, and children in swimming pools. Draconian measures that would increase our safety--like banning tobacco, prohibition, stringent requirements to obtain and maintain a license to drive, or banning personal swimming pools--actually move us away from our ideal society, not closer.
We have to "Play God" and agree that someone, somewhere, must die as a result of terrorism. We as a society already do that with our respective health care systems, with our automobils, with the sale of alcohol and tobacco, with the sale of guns, by allowing children to swim in swimming pools,and the ridiculous ease with which we allow people to obtain and drive vehicles.
The ultimate goal is to define what it means to be a Canadian or an American and then to live as much of that life as possible. The argument is whether the goal of zero airplanes downed can be achieved without compromising our Canadian or American identities.
I'll leave it up to others to argue whether strip searches and banning toner cartridges will achieve this.