Camping was been an ambush strategy in the beginning, when death match maps were entirely open ended.
The goal of any ambush strategy is to win the damage race by firing the first shot, and firing accurately. Two players already in motion are less likely to hit each other even when they spot each other.
The faster the game, the more obvious this becomes.
In order of relative speed vs projectiles/turning (slowest -> fastest)
*Gears of War -> Halo -> Battlefield 2 -> Quake 3 -> Tribes 2*
In each game, the ambush strategy becomes more powerful as the relative accuracy of the player increases (as a result of camping). In general, the faster the game, the more useful this is, because in a "slow" game, targets are already easy to hit even while moving.
The most hated weapon in Tribes 2 was the Laser Rifle. Why? Because you could eliminate targets from quite a distance as long as you camped. It was the only accurate hitscan weapon in the entire game to boot.
Of course, some games encourage camping subtly. Halo for example, has the Motion Radar that can detect incoming threats, but stops working if the targets move very slowly.
So why do people ***** and moan about camping? Because Camping is very effective when used properly. Really. People just complain because they were killed by an ambush they couldn't see coming; they were killed by strategy.
Likewise, cheap shots and low blows are always effective, but in a game based on war, why wouldn't you use every advantage you could gain?
