Of course I won't disagree that it is possible to be behind with KK (or the second nuts on any board).

Poker is a game of reading opponents and playing the odds. As stated, unless you are certain you have a super-read on someone who just reraised all-in your 4xbb bet preflop (as in, they showed you/you saw AA, or you play with the person so much you know what they will down in any situation), laying down KK preflop is tantamount to telling yourself that unless you are on the stone cold nuts (or a jackpot hand), you are willing to be pushed off any hand if it puts you all-in.

Maybe that is the smarter way to play poker, but I can't conceive of a situation (short of those mentioned above) in where I would muck KK to any bet (unless my girlfriend is the one I am going heads-up against). If I lose, I lose, and I would make the same move next time as well. If I was willing to muck those hands, I probably would play low limit games, rather than no limit.

Just my 2 cents, of course.