You can usually tell they're CoD players if they don't work as a team
While that is sadly true in many cases, I believe that some people who don't play the objective directly still camp and kill the people who are going to go towards the objective a few seconds later, and no special recognition separates those campers from the K/D ratio-obsessed campers.
But, for all the work put into camping those same people could actually contribute and be rewarded triply for playing the objective, while still keeping a decent ratio. I play CoD and I've seen many a person who gets MVP for playing the objective, myself most of the time. And I still maintain a 1.50 K/D ratio after 40,000 + kills and 3,500 defends and captures apiece. Let that be a message to the noobs out there.
I hate being put on teams with those type of players.
However, if the campers didn't contribute at all to the team then in theory you would have the same or better results if the players were not there. But that does not work, as you get owned when you are 1 vs 6 on CoD. So therefore, campers must contribute to the team in some way, shape or form. The campers on the team draw out enemies to try their luck at killing them for nothing but revenge, and therefore detract from the enemies you have to deal with. So campers are a necessary, annoying, but necessary part of the FPS gaming society should we want to continue to be able to not have to deal with 6 people at the objective the whole time.
In Battlefield, the game is much more geared towards objectives. Campers can contribute a ton more in Battlefield than in CoD if they simply put down a spawn beacon or an ammo box, but I'm not asking the 4 snipers on our team to stop covering us by killing enemies from afar to come and try to arm the M-COM with their G18's. The objective players can play their part, so long as the snipers and Dark Corner McDoogles play their part as well to the best of their class's ability.