If there's a guy on me with a knife, my last thought is about his safety, especially including what type of non-lethal method I'm going to use to disarm him. If he's willing to put someone else's life on the line, he should be willing to face up to consequences involving his life that may result imo.
I could care less if I kill a person who was trying to kill/seriously injure me for no reason either over my lack of rizla's/lighter or a few quid/mobile in self defence.
edit: This sounds a bit keyboard warrior-esque.
Seriously though, who's going to think straight when they're full of adrenaline and their life is threatened?