Cheating in anything where you are competing against someone else is wrong. By cheating, I mean using means other then those within the rules of the game to improve your odds of winning. For instance, back in the old days of Quake, when one person could easily cheat and and walk through walls/fly by simple typing "god" and "noclip" into the console, if you were playing against someone, then it is wrong to use those things.
If you're playing by yourself however, cheat as much as you want, just don't expect to experience the full experience of playing the game, and expect the game to get old really fast.
I have a friend who cheats on every game he plays. Somehow, he finds that fun. That's all fine, except when he's playing with or against someone else, then he has to man up and not cheat.