You are out of your MIND not to have sights. You can easily have to pull head shots, around cover,for instance. Even at a "mere" 6 ft,under lethal stress, sights are a big help for such.
You shoot somebody with a knife (not start the draw, but FIRE) at 20+ ft, and you are at serious risk of going to prison, for "excessive use of force". You are also at risk of being sued for everything you own, and every dime you ever make, after the criminal case is over. You are likely to have to spend $100,000 to defend yourself in court for having done such a thing. First criminal court,then civil court.
I have met Dennis Tueller, and what cops can get away with, and what you can get away with, are two very different things. If you had beaten a downed man with a club, where would you be? If you had fired 15+rds at a manwho had no weapon, was no threat to you, and killed him, where would you be, hmm? the cops who beat King, and killed Aialo, are not in prison, but a civilian sure would be. cops are defended in court by the city attorney, for free,or by a Patrolmen's Associationlawyer, also at no cost to the cop. Lawyers who are worth a hoot get about $1000 an hour, bud.