Have you ever been stung by a bee or wasp? I have. The first time I was stung I was about ten years old or so. The pain was worse than any pain I'd ever felt up until that point. But even worse was the fear, nay the terror, that accompanied the pain. What caused the pain? Was it going to get worse? Was it ever going to get better?
For the next few days after I was stung, everything that moved was potentially a bee. I was definitely hyper-aware of all insects. If a fly landed on me, I would just about freak out. However, after a few months I'd mostly forgotten about being stung and I pretty much lost my fear of bees.
The September 11, 2001 attack was like a sting. If you consider the United States as a single organism, the amount of damage to the United States that day was comparable to the amount of damage a single bumble bee can do to a person.
I'm not trying to make light of the tragic and unnecessary deaths that day. However, I think some relative perspective is important. Approximately 10,000 people die in the United States each day from old age, disease, accidents, murder, etc. Some fraction (perhaps all) of those deaths are tragedies as well. 9/11 may or may not have been a record number of deaths for a single day up to that point. 2001 was most likely NOT a record year for deaths. You're far more likely to die in an automobile accident than a terrorist attack (based on past data).
Tens of billions of dollars of wealth were destroyed that day. But that only represents a tiny fraction of a percent of the wealth in the United States. There was probably some not easily measurable impact on GDP as well. The financial markets were knocked off-line for a short period of time, but it was actually remarkably short - our systems seem pretty robust all in all.
No, it wasn't the actual damage that knocked us for a loop. It was the fear (that's why they're called terror attacks). What caused the attacks? Would we recover? Was it going to happen again? Was it going to happen often? Was it ever going to get better?
But just as the memory and fear of the bee sting wanes with time, it seems to me that our collective memory and fear, on average, of the 9/11 attacks has also waned over the last few years. I think that's perfectly natural. Perhaps even positive. Perhaps not.
Let's go back to the bees again. If you got stung while walking into your house, perhaps you'd want to locate the nearby hives. Depending on the locations of the hives, perhaps you'd take some sort of action to have the hives removed. If the hives were inhabited by africanized ("killer") bees right next to your door, perhaps you'd be more likely to take action than if it was just a small honey bee hive on an unfriendly neighbor's property. Perhaps you'd be so mad that you'd dedicate the rest of your life to killing bees. Perhaps not.
Lots of "perhapses". The point is that there is really a very wide range of subjective behaviors that one could pursue in response to being stung. The vast majority of these subjective approaches would be completely rational - they would differ from person to person simply due to personal preference weighing the cost of reducing the odds of being stung again against the personal dislike of being stung. In addition, each person's approach would change over time as more and more time elapsed without being stung again. Again, perfectly natural and expected.
As a result, there are very few responses to 9/11 that I think are actually crazy or even extreme. I may not agree with them since I'm entitled to my subjective preference just like everybody else, but I can understand the other perspectives and based on the premises of those perspectives and a little math, I can understand why others come to the conclusions that they do. That includes everything from doing absolutely nothing to extending the military action to Iran, Pakistan, and beyond and everything in between and/or orthogonal to those two extremes.
The one approach that makes no sense to me is to quit right in the middle of an operation. It makes no sense to stir up a hive, make the bees mad as -- well, hornets -- and then stop what you're doing. Once you start an operation against a hive, you've got to finish that operation, no matter how long it takes, even if that means staying there many years or even decades.
Stopping in the middle of the operation is exactly what were getting dangerously close to doing in Iraq. I'm very confident that is a very bad idea. I can see the merits of almost any other approach. But not that.