Using knife is like announcing to everyone who are even remotley close that you want to die. It dosen't have to insta-kill, but im under the impression that it's supposed to be silent. Instead it just makes a light-saber sound when you pull it out, marking yourself for death. My suggestion is to remove the sound from equipping the knife. It's still easily visible for people that look at you & bodies that fall down make easily detectable sound for anyone who listens. If you think its too op when its silent just increase the ammount of time for DNA to expire from the body after getting stabbed.