What's wrong with the FAMAS?
Ever played CoD4? It's the M16 resurrected. With stopping power, one burst is lethal to the chest or head, possibly even the legs or arms. So, if a guy with a FAMAS see's you, unless you have the FAMAS or another one-shot kill weapon, you're dead. People with the M4, or hell, the SCAR-L or Tar-21 will lose every battle if both people fire at the same time, in the same place.
I've seen snipers using thermal scoped FAMAS instead of a real sniper rifle, because the FAMAS offers one-hit kills, essentially no recoil, and a large clip. Don't believe me? Play a game with the FAMAS, check your score, then use the M4, or some other assault rifle, don't leave the server, and see how well you do. I will admit, when I use the FAMAS (the first three levels after prestige), it is fun owning tons of people, even if it is damn cheap.