> "Preventing all terrorism" is both impossible and wildly impractical: to even get close, you must eviscerate the freedoms in your society and undermine the rule of law.
Preventing all terrorism isn't actually the goal though.
Just like our vaccination regimes are not intended to completely eradicate disease, merely prevent epidemics and pandemics, the anti-terrorism programs are intended to increase safety and security for Americans (and by proxy, other nations who would also be targets of the groups aligned against the USA), in a way such that terrorism does not happen so often that the people demand the police state we all claim here to despise.
It is recognized that completely eradicating terrorism is probably impossible, but the U.S. can make it almost impossibly difficult to form large enough terror cells to repeat things like 9/11.
And unlike your rather defeatist attitude, I think that can be done without "eviscerating" civil liberties, as long as we employ ample doses of transparency, watchdog groups, and organizational structures designed to keep those programs directed to the mission and provide accountability and oversight. Of course it can be done; how do banks holding billions of dollars of their customers funds manage to provide strict accountability for those?
Pretty much every prior technological breakthrough has made tyranny in the U.S. more likely, and the U.S. has managed to pull through in each case (though sometimes with roadbumps...).
And, if you're really concerned about the rule of law you will do everything possible to avoid "a 9/11 every year". When the state fails to protect the people, the people (armed by the 2nd Amendment) will take matters into their own hands, and it won't be pretty for many innocents in America.
But again, if you have better ideas I'm sure the NSA is listening...