I think it is widely perceived among the folk (and widely approved, as well) that one aim of the war was terror in the sense of unpredictable death and destruction upon people even remotely associated with the target group. At least this is what I pick up from the office, the street and the media. Therefore, there was no need for the wrathful among them to go into the streets and perform DIY terror; the government was ready, willing and able to do it for them. As some said at the time, "We gotta do _something_."
I have to note as well that, if a major terrorist act resulted in a great advancement in power for a power-desiring party, they would not _thereby_ be dissuaded from activities and policies which might result in further terrorist acts of the same sort. A sufficiently abstract view of the Realpolitik might see a moderate exchange of terrorism and war as an ultimately good thing, leading to a more secure world order through the extermination of violent dissidents at a cost acceptable to the elites. Of course nobody we know would ever think in this way.
-- Gordon