Cheating and baseball have gone hand in hand for as long as the game has existed. Stealing signs isn't a new phenomenon, nor is it likely to go away anytime soon. Pitchers have tried to doctor the baseball for years and well... there's that steroid thing. Mauer's blatant sign-stealing will likely go unpunished, but is that right? I say yes. MLB will never be able to catch everyone that steals signs and in addition, I don't know if there's a rule prohibiting it.
Stealing signs is a part of baseball. Does that make it right? No, but baseball is unique in the sense that it has its own internal discipline. If the opposing team suspects sign stealing, the culprit is likely to get plunked in his next at bat. While Mauer didn't get hit by a pitch in retaliation, the possibility is there. When it comes to sign stealing, it's best to let the players deal with it in their own way.