I must agree. Absolutely no cheats should be allowed in any multiplayer game, I don't care if it is pong, or renegade, there should never, ever be cheats for multiplayer games. Sinlge player- That depends. Id say, if you are one of those people who is completely impatient, you get pi$$ed at everything, and you have at least tried the level a few times... That is understandable.
HOWEVER, if you are one of those people who enters their clever little cheat code as soon as a mission starts, and you havent even previously tried the level on your own, you should rot in hell. Pardon my offensiveness, but thats my opinion.