Ok, so just to play the devils advocate i am going to make a list of the most hated things in MW2 and explain their reasons for being.
Nube Tubes: Dealing with the guy camping in the house on estate with his acr.
OMA: being able to change you kit to deal with air support, snipers, or what ever else might come up. (yes it can be used to have constant nube tubes, deal with it)
Painkiller (and deathstreaks in general): instead of fixing the spawn system IW made it so that people getting spawn killed got a health boost, it backfired, but it was an honest effort none the less. (treyarch take heed, fix the spawn system)
Customizable killsteaks: some people hate em, other love them, but i bet if you and everyone on your team ran UAV, Counter UAV and airstrike you would do better than the cuy camping in the house with OMA harriers ac130 and nuke. im here to support the customizable killstreaks.
Not 1 hit kills with sniper rifles: Sniper rifles should not be a one hit kill if you shoot someone in the arm, it would unbalance the game, i notice the only people who complain about this are those crazy run and gun quickscopers and no scopers, lemme give you a hint, aim for the body. or go play hardcore.
Shotguns and Machine pistol secondaries: this is something that many people complain about but i dont think it is unbalanced, it takes longer to pull these weapons out so they are less useful in the situations when you really need to use your secondary, that is when you are taking on a bunch of people and you run out of ammo for you primary and there is still one guy alive.
Commando: No reason whatsoever, this perk actually needs to be taken out of the game it makes the person with commando comparable to someone with an energy sword in Halo.