"Instant-Failure Stealth Levels. Ack. This brings back horrible memories of a Goldeneye level where if you tripped an alarm, an infinite number of bad guys poured forth. We knew a man who failed that level 37 times, then got the Infinite Health cheat for it and came back. He intentionally tripped the alarm, the guards rushed out. Laughing maniacally, he proceeded to shoot those fvckers for four hours, killing 1,183 of them - 682 with groin shots - before his thumbs cramped up. Your game should not create this kind of bitterness."
I did something like this myself
I enabled laser for the weapon and invincibility.
I went to facility, tripped the alarm, and set myself up in a room where guys would come to open the door end get shot.
I put a rubberband around the controller to hold down the trigger and left the sucker run overnight. I don't remember what the death toll was, but it was impressive.
EDIT: #14 is awesome