To put this in perspective, if EVERYBODY camps the game makes no progress and ends in a stalemate. If everybody rushes, the body count is absurd but a victor is found. Thus, in the most basic sense, rushing is superior to camping.
Let it be said however that many game modes need a certain percentage of the players on a team to camp unless said team possesses dramatically superior skill and ability to work as a team. Somebody has to slow down the opposition as they approach flags in domination for example. Even in Team Deathmatch the camper has a place, albiet an unpleasant one. Staying still often allows one to score easy kills, and in some cases may represent the only real hope of getting more than a few accidental kills a player has. It must be said that either extreme has it's flaws. Running into knife range will often get you shot in a hurry if your opponents are paying attention, and you are consistantly thrust into situations where enemies may appear from more spots than you can possibly counter yourself. The camper on the other hand is often alone in a place with two or even three entrances to cover and only themselves and perhaps a claymore to watch all of them. What's more, the static nature of the play style inherently means one can simply avoid them, or bypass the most reasonable avenue of approach and get an easy kill.
I would like to iterate once again however, that, at one time at least, there was a distinction between a camper and a defender. Back in the early days of online gaming (quake 1 for example) there were few pure DM maps - most were repurposed single player levels. As a result, from time to time one would be given a room with only one entrance with a desirabe item located inside (usually health and/or armor). Camping refered to the sort of player who literally sealed themselves inside this room with a rocket launcher pointed at the door. Since deathmatch was the order of the day, and since it took cooporation between multiple players to resolve the problem. camping was seen as the lowest form of gameplay.
Sniping has only relatively recently been considered camping since the job is often static in it's very nature. Certainly one does not expect the player with a single shot rifle to rush into the melee after all. The trouble I see with snipers in MOST games is they rarely actually further the team objectives. In many games, simply shooting people doesn't really accomplish anything other than inconviencing a player for a few moments. In games like Battlefield, I rarely saw snipers overlooking the enemy spawn or a friendly point, instead they would hide in the middle of nowhere and rack up meaningless kills. This sort of activity is still not camping in my book but it is fantastically annoying. They do nothing to further the objectives of my team and simply annoy the opposition and I have no use for such nonsense.
Of course, in modern games, often some sort of static objective is at stake. This could be a flag (CTF) a point (king of the hill) several points (domination) or some other high value target. Obviously these points need to be defended and the most logical thing to do is stay nearby. That said, in many games there are natural approaches that most players follow. Is a person lingering nearby to be considered a camper or a legitmate defender?
The trickiest thing is in games like MW2, the maps are quite tiny and there are distinct avenues of approach that can be controlled. A single skilled static player can utterly close off an avenue which is a boon to the defender's team. Because of the nature of how the maps of designed, there is always an alternate route and the camper can certainly be dealt with easily enough, even by a single player. It seems to me that level design alone has eliminated the camper as a problem in modern games and as such the static defender has taken on the title. No matter how irrating a camper can be in modern games, it doesn't hold a candle to the activity that spawned the name.