It sounds like you have serious issues then, if upon realizing that you can get away with doing something unintended, you suddenly find yourself constantly thinking about doing it.
You can probably get away with planning and robbing your neighbor in "under a few days' worth of time", and you'll probably come out with a lot more money/valuables. But I hope, now that you know you can do it and get away with it, you're not suddenly thinking about the "what-ifs" in the back of your mind all of the time.
I don't think most people seem to have the same problems with compulsiveness that you are having...
I think that's a little insulting, but I do agree that I'm not ordinary. However, your analogy is flawed: modding my save hurts no one but potentially myself, while robbing my neighbor hurts them. Morality need not come into play when modifying your own property, while morality would keep you from taking from others.
I'd argue that I have the same thoughts about modifying the vulnerable game as someone that does do it; I just have extra desire not to do it, knowing that it will likely make my experience worthless, aside from some initial amusement. For this reason, the thought of doing it remains, because I never give in to it.
that's only because you have the knowledge necessary to hack it and therefore look at it from a different (larger) perspective.
its like me when i see a movie now that i've become a gamedev, i can't enjoy the flick, cause i'm always thinking about camera angles and graphics sfx. I have to watch twice to get the story.
you can't simply enjoy the toy as a toy, cause you build them yourself, and are always thinking about how its made - or not made - or how to hack it to make it better - or how to make a better one of your own.
you have to remember is just a game, not a hackers challenge.
I do agree, that is a big part of it, but non-game devs can relate: Who has owned a GameShark? I know a lot people that are not programmers or able to produce anything, but know how to open a text file and add numbers, so this instance doesn't require any knowledge.
Now, I'm not above modding. I remember modding Worms and GTA III long ago, among others, but only after the game was finished, and no more fun could be had. Heck, if you want to have an unlockable feature that gives you the decryption key, cool.