I don't think K-J is a bad hand. This is another one of those hands that so many players seem to find problematic, that I simply don't have a problem with. Like any other hand I win with it sometimes and sometimes I lose with it. And like any other hand, I try not to get too carried away with it, so losing a hand doesn't mean losing my entire chip stack.
I have to wonder if the problem people are having with this hand has anything to do with the way it's being played. I see where a lot of players are saying that K-J is a good hand to limp in with. I disagree. I don't think any hand is a good hand to limp in with. Limping in means you're allowing more opponents the opportunity to see a cheap flop. Playing a hand against more opponents reduces your chances of actually winning the hand. Playing any hand this way is going to be problematic. At the same time, I see a lot of players ship all their chips into the middle. Again, playing any hand this way, not just K-J, is going to end up being problematic.