Rrrrrrrright. I can't imagine that you'd ever considered the possibility of a struggle between a hijacker and a pilot and the consequences what might happen...
The common sense point of arming the pilots is to AVOID struggles for the cockpit. -- They shoot the bad guys as they try to come through the door.
But you are right, I can't imagine the next 'what if' possibility you'll come up with. - And don't really want to. -- Thanks.