Camping is only ok when it's in certain situations.
If you're a sniper, then it's fine. Nobody expects you to run out and use your single shot weapon like an assualt rifle.
If you're defending an objective, once again, it's fine. You're supposed to stay there and defend it, that's your objective.
If you're outnumbered, camping is fine. On more than one occasion while playing COD4, I've been alone against 2 or 3 enemies, sometimes more on a certain part of the map all coming from the same direction. I can't be expected to run out and engage them, so I get into a stategic position, take them out and move on.
And finally, camping behind cover for a few seconds to get your barings or take out an enemy is fine.
The camping that does nothing but piss me off is when a guy is in a darkened corner watching an area with alot of traffic with a heavy machine gun, usually in prone. On COD4 add juggernaut and last stand to the equation. It's alot more common than you'd think. There's no excuse for this shit. I don't care if you wouldn't run out in real life because this isn't real life. I don't care that you want to preserve your K/D ratio, because it doesn't matter, it's just some numbers that have no real meaning to them. Frankly, if you care that much about your K/D ratio that you have to camp and probably bore yourself half to death, then you should be doing something else because you're doing nothing but ruining the experience of the game not only for yourself, but for everyone else in your game.