All right, what's with this "easy to destroy" thing?
Think about what you're saying. Don't you think it would occur to the people that these devastating uberbeams would make great targets so the designers might more heavily armor and protect them than they would another turret?
*Stops, realizes he's making unfair assumptions as to the intelligence of GTVA Command*
Any NORMAL person or group would realize this weakness and harden the turret through the addition of more anti-fighter\bomber defenses around the beam. Besides, have we forgotten that we have to mount these on big ships.
Big Ships With Fighterbays?
I mean come on! And I know someone is going to bring up Trebuchets, so here's my solution to that: EMP missiles. Shuts down warheads in flight.