So long as they aren't spawn camping, there is nothing wrong with it at all. Campers are easy to deal with if you know the map you're playing on, and even easier if you just take a friend with you (even if he takes out one of you, he likely won't be able to take out both, since the element of surprise is gone). A good camper will constantly change his ambush positions every kill or two, which arguably doesn't quite make it camping, but the idea is the same - stay more or less in the same spot(s) for the whole game and take people by surprise. In the case where a camper is more or less impervious to attack, has a clear view of the enemy spawn, etc., then you have a broken map on your hands. That's one thing I hate about Call of Duty's multiplayer - there's no designated spawn zones, so you're very likely to get bombed to oblivion by an air strike as soon as you come back to life, only for it to happen again a second later.
