Okay, I understand where this could be abused, but it is realistic (to a degree) to have the guns operational. Maybe have just the top gun or tail gun active on takeoff would be a compromise.
I'm thinking of the other day when we only had 4-5 fields, always under attack, and trying to get a decent buff mission going (which isn't saying much since I really suck at buffing). Taking off from a 'rear' base was just as bad as a frontline base.