Copyrights and EULAS are meant to protect the investment in research and development that went into a particular product.
The demarcation of that ideal is evident in software such as Windows, Office and a myriad of other offerings.
When it comes to games (which I do not play) the demarcation evident in my above statement can become less clear.
If cheats degrade the intent of a game giving priority to those aware of the cheats or able to buy them, a game maker has a right to seek redress. So do those that bought the game only to find themselves disadvantaged in game play because they chose to play by the rules. I'm with Trucidation on this one and I'm not even a game player.
DISCLAIMER: I have cheated on Pinball, Minefield and Duke Nukem.
(but never in a multi-player environment)