Err, no offense, but that's not quite true.
They are "projection of power". Sort of like parking an M1A1 MBT near your house. You're a lot less likely to get robbed. Terrorists will go where the prey is easier. They are done with airports for as long as we continue to have a power projection there.
Thing is though that other than a terminal attack the massive police/military presence does little to help the risk factor. It LOOKS nice, but it doesn't make much difference if the Terrorist walks in through the employee entrance...
Regards,
-Bouncer-