Every FPS has campers... and two types, neither of which bother me.
Camper 1: New to the game, afraid that as soon as they run out of the building they're going to get murked. So they stay glued to the window with their shock charges / BB set up at the entrances. There is no excuse to die from these guys more than once. They kill you, EMP the room run in and kill them. They're camping because they can't do CQC so it's not an issue.
Camper 2: Experienced player with fast twitch reflexes and fair amount of strategic positioning as well as knowledge of the map. There is no getting them to move unless you get lucky with a grenade or happen to get the drop on them (which usually is near impossible). These guys will kill you over and over and over and they're all free kills because by the second time you die you're too pissed to play well and they know you're coming. I usually leave them alone and run a different route on the map, doesn't make sense to keep dying needlessly to prove a point. They don't bother me, because they're better than me.
Camping is a legitimate strategy in all FPS games. There's a diff between camping, and finding a hiding spot and waiting for someone to run by and not notice you because you perfectly blend in with the bush you're crouching on top of. Either way, shouldn't be frustrating... either find a new route or get rid of the guy hiding