I don't think you can assume the legalities are done away with. I didn't assume it in my answer. You certainly can't assume it in the real world.
The issue is at what point in the sequence do you draw your gun. If you draw and shoot all or any BGs before they draw, you're in legal trouble. I'm licensed to carry a gun, not stop crime before it happens. If you wait until one or more draws, you're in even more trouble, if you're still in the room with a holstered gun.
I hope some more folks weigh in on this.