Oh, and one more thing. Nothing is sadder that seeing a team of 6 lvl 6 players huddling in a corner shooting down a hall while two guys keep a door welded. They only learned how to play in a barricade so that is all they know.
Now the completely legit question: what's wrong playing more defensive and campomania style? Running around bat**** bonkers and going for "I steal kills by spamming with the M14 and then my e-penis grows when I have 1000 kills u noobs" can be amusing and even fun on some occasions but by the time you've seen gazillion wipes because people are not aware of their surroundings - and most of them seem to be sharpshooters for some unknown reason when they're running around - it becomes more silly than saying it's the right way to play.
Going with the "playing the right way" or "doesn't know how to play due X" argument doesn't really work as much as there might be some point behind it. Otherwise one could easily go that unless you've killed FP (post-instadecap) with a knife only without dying and no 3rd party help (nor weapons) you don't know how to play the game.