I asked in Black Ops I & II, and I'll ask again here:
Please remove panic-knifing in future Calls-of-Duty.
I think that the vast majority of players are just irritated by the function. It lowers the skill-ceiling and rewards poor tactics & foresight.
The argument of its' being unrealistic and silly doesn't hold much weight in a game as simple and arcadey as COD, but it's still true.
Having the Tac-Knife as a primary would still give the people who want to melee it up something to play with, but the panic insta-kill without having to draw it or even have it equipped is just terrible.
Thanks for considering,