I guess I don't see the big deal about sign stealing. I mean, in some sports, maybe stock car racing or something like that, this kind of thing would be totally encouraged. Squeaky clean compared to doping and what not.
However, cheating to win still takes something away from the game. But fundamentally, any sport is based on the principle of a level playing field... that everyone is playing by the same rules. This isn't a case where they stretched the rules, or went right up to the line -- they gained an undeniable advantage using tools that the other teams didn't have. When the batter know the pitch that's coming, you take the most competitive aspect of baseball away.
For my money, baseball teams should pursue simple encryption schemes where the sign thrown has to be decoded by the pitcher in his head, using as additional parameters the inning, batter, and a special private key agreed upon by the pitcher and catcher before each game.
It's using electronics to steal signs that is against the rules. It's because electronics basically allow you to "perfectly" steal signs, and one of the biggest things in baseball is that the batter doesn't know what the pitcher is about to throw.