Jon spoke those few words. "I wish that when I hold this stone that the wishes I make would be unlimited by any means."
And suddenly odd thoughts filled his head. He could get payback at the bullies at his school, heck even at people who look at him wrong. Thoughts of hurting others didn't feel bad anymore. he can make a sex slave of Karyn, of his dad, of his little brother, of his dog, of the tree outside. None of these thoughts bothered him. He could become a guy, a girl, a rock, a grizzley bear, none of that felt wrong to him either, at least as long as he makes sure he can wish again if need be.
Jon had an evil grin cross his face. Thoughts that once would have gave him pause or make him shudder in fear no longer did so.
The stone answered Jon's wish by removing Jon's limits. He no longer had such silly things tying him down as morals, fear of repercussions, conscience, or disgust. He could do ANYTHING he wanted and their was nothing that was beyond his want.
Jon's wish had unleashed a monster and that monster was Jon. Jon without any mental limitations. The same mental limitations that make most people sane. The world was Jons to do as he wished with and he had no self imposed limits to what he wanted.