A couple of thoughts...
Was this beneficial result that you mention worth the (ongoing and open-ended) cost? Note that in World War II, the benefit was clear... survival itself.
Also... have we really deterred future attackers? What about terrorism? That's how this latest session of perpetual war started, isn't it? Are Islamic terrorists deterred by our forcible disruption of an Islamic country, or are they inflamed to new heights of rage? Should we even care about this? I think it's a fair question, since the president cited containing terrorism as justification for war.