There have been several instances where people seem to mix up the difference between camping and sniping. So let's get this straightened out.
Sniping: Sniping occurs when you find a location on the map that allows you a vantage point where you can fire on players coming through a chokepoint, such as an alleyway, doorway, etc. Sniping can also occur when you find a corner or other area where you can fire on players without being easily spotted.
Sniping is a valid gameplay practice and combat tactic used by militaries across the world, obviously.
Camping: Camping occurs when you find a location where you can fire from without the possibility of players returning fire. This usually involves finding a location within sight of a spawn area and killing players before they are able to return to the play area, but can also involve finding a location such as a crack in a wall or small opening in a balcony where you can fire from, but players are mechanically prohibited from returning fire or otherwise cannot avoid dying.
Camping IS NOT the same as sniping. Camping is an abuse of gameplay mechanics, is unfair to the enemy team (and often to your own team, since you're depriving them of kills), and ruins the game for everyone except you, the camper.
"But Hat Guy, if it's in the game..."
Shut up. Lots of things are in games, that doesn't make them fair. If I somehow had access to a dev console in multiplayer matches, would that be "fair"? No. Not in the slightest.
"But Hat Guy, camping is a skill just like sniping..."
No. No it isn't. Sniping requires knowledge of the map and knowledge of how players tend to navigate it. It requires actual talent to be a good sniper in real life and in the game. Camping doesn't require anything except a knowledge of where the game is going to spit out players after they die. That's not even close to the same.
"But Hat Guy, camping is fun..."
Only to you, you jerk. It ruins the game for everyone else. It ruins it for the player you're repeatedly spawnkilling, because it wrecks their KDR and means they can't play the game. It ruins the game for the enemy team, because you're getting kills for free, and they're still having to work for theirs. And it ruins the game for your team, because they end up either not getting to play at all because everyone's dying at spawn, or it makes the game too easy, because there's a bunch of them and only a few enemies at a time.
TL:DR: If you're a camper, you're a dick. It ruins the game for the hundreds of other players who paid money to actually play a game, not sit there and get spawnkilled repeatedly. Either get good or go play on a private server somewhere with other like-minded dicks.