That doesn't contradict me; it's consistent with my claim, in that (some of) the post-9/11 countermeasures sufficed to raise the difficulty threshold. I'm trying to make the point that there's a difference between random and intelligent/adaptive causes of death. Thieves attack security holes once they're made known, while bathtubs don't somehow become "more drowny" after the first person drowns in one.
The argument I'm criticizing -- that you should change nothing merely because terrorism is a low fraction of deaths -- is actually rejected by the frequently-cited Bruce Schneier in the essay you linked. He advocated -- as I do -- that we change something in response to 9/11, specifically the cockpit doors and the hijacking compliance policy.
Next time, it might help if you put the argument your own words; when you only link to a massive document, I don't know which point you're criticizing and it shifts an enormous burden over to me without making it easier to identify the point of contention. Also, the headline is "terrorism is not effective", which is hard to reconcile with the several mass-kill attacks, and which doesn't appear to be related to the point you were using from it (that countermeasures are irrelevant in light of lack of motivation).
So I ask again, what are you criticizing? I agree that terrorist attacks are a small fraction of deaths, and most don't succeed. I am claiming it does not follow that nothing should be changed after an attack. If you have an argument against that, please explain why, as that would justify reversing the cockpit-door and passenger-noncompliance policies.
If you agree with those post-9/11 policy changes, you were agreeing with me the whole time.