Hmm.  Well that's an argument usually used by those hell bent on removing civil liberties and repeated by those who haven't thought too hard about it.  Its fallacious of course. 

We've had one devastating attack and one thankfully bodged attack.  Neither of which would have been prevented one bit by the new legislation.  To argue that its one or the other ignores the fact that ... well ... it ISN'T one or the other.