There's nothing wrong with camping, it is a perfectly valid tactic. Especially in games like COD4 or the Battlefield series where running out in the open will see you killed in seconds.
This is especially true with snipers. It's basically their job to find a nice spot and sit there picking off enemies. A sniper that moves every couple of minutes will just be killed horribly by someone wielding an assault rifle or similar.
I personally play as a sniper or long-range marksman type quite often in games like COD and Battlefield, and nothing is more irritating than sniping the same person who was stupid enough to try and run past your field of fire for the 10th time that match only to get gunned down again and then shout something like "OMG NOOB CAMPER!" Well, I'm sorry, but if you can't learn to not go back to the same place you've just been killed ten times in a row at, or notice the person whos been sitting in the same spot for ten minutes, well then it is YOU sir that is the "noob", and if you have the audacity to try and call me a cheater for hindering my own mobility, I will very quickly lose any respect I had for you.
In my experience at least, camping effectively takes the same amount of skill as running about everywhere as well. You have to continually check your flanks to make sure that no-one is sneaking up on you with a knife, and you have to be on the watch for counter-snipers that may be lurking below waiting for you to fire and reveal yourself.
Now, I agree that those that sit in the exact spot for the entire match even if there are no enemies in that area can be annoying. Whenever I'm camping and havn't had any activity for a few minutes, I go to find a new spot closer to the action from where I can support the rest of my team. For example, in BF2142 the action regularly moves around the map as your team captures and loses command points. I may camp somewhere near the first neutral point at the beginning of the match for a few minutes to watch over it and snipe any enemies that try to cap it before the rest of my team get there, and then once it's secure I'll move on and find another spot near an enemy CP where I can snipe any enemies guarding it and allow it's capture.
I do of course recognize that a lot of players find camping annoying, but I really don't get it. Spawn-camping yes, that is terrible, and I've been on the brunt of it many times in certain matches of COD4, but in general I don't know why people find camping so bad.