I do armed security at federal facilities, some of them crowded. In the case of an active shooter, observing rule #2 and withholding fire "because there is a friendly behind the target" wouldn't make any sense. The bad guy would kill me, take my weapon, and continue his rampage. Sometimes it's neccessary to shoot even if the life of an innocent is at risk.

(I'm designing a "poppers in front of a NT" CoF right now, and found this thread.)

Harry