-snip-
Wait, what kind of "prevention" are you talking about here? Just curious.
Preventing terrorists from getting explosives into the US or making them here, preventing foreign terrorists from easily gaining entry to the US, making it hard to obtain improvised weapons, and preventing terrorists from becoming powerful by supporting nations in fighting their own local terrorists. That last one is different from sending our own military in because that costs more and involves sending a large portion of our army to fight and die in a land they don't understand.
I know its a cold viewpoint, but the amount of people killed by terrorists annually in the US is tiny compared to other societal ills like medical problems, our own military operations, or plain old murder. The terrorists had their one, utterly horrible moment in 9/11, but since then weaponizing planes has become much harder and the terrorists haven't caused any disasters on nearly that scale. Yes, as long as explosives or dangerous vehicles exist there will always be the possibility some crazy guy will use them to kill. But you know what? That would still be true even if every Taliban and Al Queda member suffered a fatal heart attack right now. Life is risk. And I think that in this case the sacrifices in terms of military casualties, government expenditure, and creepy totalitarian legislation have outweighed the risk of staying reactive and using a measured response.
I like to compare it to crime. You can't attack crime, because ordinary people can choose at any time to become criminals. Criminals will always have the initiative, always choose their battles. Same with terrorists. Yeah, both terrorists and criminals will form organizations, and some effort should be made to stomp them out. But I wouldn't want the US to suspend due process just to take out the Mafia, and I certainly wouldn't want them to attack Italy because its a Mafia stronghold. I don't see how the Taliban are different; they're resilient, rely on local knowledge, and are ultimately a bad but livable plague on society. Except that unlike the Mafia, the Taliban doesn't have a strong foothold in the US.
(this is all the view of a US citizen, if I lived in a country actively plagued by terrorism I would definitely want a more military response. But even then I think reactiveness and longevity are the name of the game when it comes to fighting terrorists. You know, in my experienced college student opinion.)