The rumor of camping being a legit and smart tactic can be easily destroyed by two facts : one , if everyone played like that then the gameplay would become frozen, static, and two, there is nothing smart and tactical in hiding and waiting for people to come to you so you can get a easy kill.
Some also say that camping is necessary,as noone would run around in real life in a real war. Those people are usually mentally ill becoz they seem to associate a game with real life , so they are to be ignored.
The stupid camper usually picks a random spot ,without taking into consideration if he has good cover, if the area is of high traffic, if it's near an objective or anything else, and he just sits there without moving. Those are usually easy to be killed , as if u get killed by them once u already know where to find them becoz they're not smart enough to move.
The smart camper is a whole different story. These people were born to camp and they camp for dear life. They have tactics ,tricks and determination in what they do. A smart camper usually picks an important area where people pass trough often , picks a obscure hiding spot where he is hard or impossible to be spotted and wich also provides him with good cover, chooses a suitable close range powerful weapon,such as a shotgun and usually aims down sights at all times. He also claymores the area up and from time to time switches corners. Usually they can be killed by throwing a flash or stun grenade before going at them or just noobtubing them out.