In this case I would say that the service department is to blame for even suggesting that you drive the car with a known safety-related problem. Maybe it was just an honest oversight or maybe they were being stupid but when they said that they crossed the line. Of course, the correct response to that advice would have been to say that the car is not serviceable (assuming you need to drive at night) and you will not drive it The factory warranty provides for a service loaner so if the service dept is telling you that the car will be awaiting parts for three weeks then it should be a no-brainer. Stick to your guns and tell them you want a loaner vehicle. Yes that new SRT-8 sitting on the lot will do just fine.

Funny coincidence: When an aircraft is not in serviceable, the US Air Force refers to it as a "Red X".