Security services themselves need to grasp this, to avoid deploying hundreds of operatives and millions of pounds (dollars) on investigations which in the final analysis do not add up. Essentially, they need to start doing risk assessment and to stop over-reacting on the strength of 'might'. While they're chasing 'might' they can all to easily be neglecting a whole stack of 'wills'.
Oh, but where would our media be without the Movie Plot Terrorist Attacks!? Can anyone recall when our own White House suggested folks wrap their homes with plastic wrap and duct tape? Local hardware stores ran out! I suggested a smaller, personal protection system -- seal yourself in a trash bag -- but no one would take me seriously.