The Taliban protected Al Queada prior to 9/11, too. The reason we didn't attack the Taliban prior to 9/11 was because we concluded, wrongly, that it wasn't a threat to us. Fortunately, having learned our lesson the hard way, we didn't repeat this mistake with respect to Iraq. That is sophistry. What is your argument? That because we failed to see the threat of 9/11 from the AQ forces residing in the Afghan Taliban regime that we are now, somehow, empowered to destroy any percieved threat anywhere at anytime on the Globe? That is precisely what scares the world about the USA. And what is driving us into over extension and creating more terrorists.
We were attacked on 9/11 - not with WMD's (a Threat I lived under most of my entire life and so did my parents from madmen like Stalin and Kruschev and Brezhnev and Mao) but with box cutters! With box cutters.
My argument is that we have every right to take proactive action in self-defense against terrorists and the nations that engage in, support, or harbor terrorists, up to and including the use of military force when it is in our national self-interest to do so. We need not wait until the next 9/11 and the deaths of thousands of Americans (or more) before we protect ourselves. The only people who should be scared are the terrorists and terrorist nations themselves -- and that's exactly the way it should be.
Incidentally, we were indeed attacked on 9/11 with WMDs, not in the form of box cutters, but in the form of Boeing 767 jets loaded with jet fuel.