Every shooter is about camping and is basically a game of tug-of-war over map control. Your goal is always to engage an enemy in combat when you are in a superior position. However, there is good camping and bad camping.
-Good camping
You run out at the start of the match to take a key strategic map point and then you camp it while trying to push up little by little to control even more of the map. You want to camp a route to the objective somewhere between the objective itself and the enemy spawn. You want to stop the enemy BEFORE they get to the objective.
-Bad camping
You don't run out at the start of the match and you start camping right away just trying to get kills. By not running out and trying to take the mid-point of the map at the start, you are basically giving the enemy team map control for free and only making it harder for yourself to win and also get a good KDR. Bad camping actually makes getting a good KDR harder, which is the goal of camping. It's not good for you nor is it good for your team. Also, you don't sit at the objective or behind the objective and camp it, you push up past the objective and camp a route to said objective. It's only a matter of time before an enemy push will wipe out your team, isn't it better to get wiped out in front of the objective so you can spawn in and have a chance at stopping them from capping the objective vs being wiped out at the objective point and having no chance of running back to stop them from capping the objective? Playing the objective is keeping the enemy as far from the objective as possible as every shooter is simply a game of tug-of-war for map control. If you control the map, you'll get the objective.
Anyways, people hate (bad) campers because regardless of what team you are on, they make matches boring and noncompetitive. If my team is full of campers, then my team will get pushed back to our spawn and it'll be a frustrating match. And it's even more frustrating to lose when your team didn't even try to win. If you're on the dominating team, it's boring trying to shoot people camping in their own spawn and afraid to come out and "play".