Good point. I should've substituted "prevent" for "deter." There's at least one possible way I know that may prevent future terrorism: kill the terrorists (although as others have pointed out this is far from a certainty). Of course, it's an open question as to whether more misery would result from that course of action than would be prevented. I'm leaning towards an equivocal "yes," especially with Bush's premptory declaration war against an enemy we haven't even conclusively identified.
-- Luke