BOING is spot on, don't be too hasty to shoot the security screeners, they are merely doing as they are instructed, and are under enormous pressure to keep the passenger throughput at a maximum.
As has been stated, their instructions come from their own management, and their instructions come from the appropriate Governmental departments.
I agree that it seems farsical to confiscate nail clippers etc, (last year I had the pin from my Rememberence Day poppy taken from me), but who would be the first to be blamed when such a small item lead to an on board security incident?