"I find it interesting that 3,000 lives lost in a single attack is an over-reaction, but 3,000 lives lost on the battlefield is a horrific tragedy that indicates we're in a horrible quagmire and losing badly.
Ironic.
That said, I think the professor makes a good point; indeed, I've said most of the same things many times myself, including on this blog.
The answer is: First off, if we aren't more vigilant, we will see more attacks like 9/11. Second, increasingly we are seeing development of technologies that will make mass killing by the thousands cheaper and easier than ever for lunatics. Third, we have to face the fact that there are regimes which sponsor terrorists and do something about it. Fourth, while it sounds bloodless, it's just a fact that the damage to commerce is as big a part of this as anything; if our cities are not considered safe, then all our lives are affected. (When America went to war with the Barbery Pirates, it's doubtful that more than a few hundred American lives were ever at stake, but the cost to our commerce system was substantial.) [ I'm not that Dean is counting the number of Americans -- but admittedley especially Europeans -- that were enslaved by the Muslim pirates. This was no small deal. (Also see this.) Plus ca change... -ed. ]
This is why 9/11 required fundamental changes at multiple levels--which it changed everything. I'm finding it depressing that we have to rehash those arguments all over again but perhaps we do."