This isn't a new or unique problem, and many games have had to deal with similar issues. There are generally two directions a game ends up going:
There's games like Grand Theft Auto where you can gleefully plow down a sidewalk of people in your car. That's going to be rated by the ESRB and it's "obvious" enough to make news headlines. You don't need to use your imagination here...there's clearly an old lady rolling off your hood, and it makes for a powerful argument against violent gaming.
Then there's games like The Sims, an innocent and family-esque game on the surface. However, I have the freedom to do whatever I want to my little Sim guy. I could decide, for example, to remove all the doors in my sim's house and watch as he slowly withers away to nothing. I can kill his entire family in front of him and force him to stand in a puddle of his own urine and eat spoiled food just to survive.
Now those parts are not rated by the ESRB (Sims is rated Teen) nor do stories like those make headlines...usually. Nothing in the Sims is done graphically or in a way that'd offend. Your sim starves but he doesn't fall over and die. Instead he has a talk with the grim reaper and becomes a friendly ghost. Everything is done in an almost comical way, so it's up to gamer and his imagination to "fill in the details". The implications of his actions, however, still remain.
"Not to be afraid, my love, this game is rated E! What's the worst that could hap-"Scribblenauts takes a little bit of both approaches it would seem. Like the GTA series you're going to find yourself in some very obvious "bad" situations. Strap some TNT to a cop then glue him and a puppy to a nuke. Yeah, pretty obvious I'd say. However, the way it's actually executed is closer to The Sims in that it's in a comical and "innocent" way. No one really dies, they justdisappear. The largest amount of graphical violence we'll see is the little emote people make while fighting.
Thankfully we have nothing to worry about from the ESRB. All they care about is the lack of graphic violence, the fact no one is gushing blood, and the lack of vulgar items. But like the title suggests, I'm not worried about the ESRB. I'm worried about the general public.
But it's the imagination that takes that concept and makes it a lot more real and a lot more...dangerous. I wonder what, if any, backlash we're going to see. Everyone is excited that you can do literally anything you want in this game...I just wonder if they realize that some people might not want to do very good things.
Finally, it starts going down some rather dangerous paths...can we police the mind or the imagination? Can the ESRB rate a game based on what a person takes away from it, not what is literally going on the screen? Hmm.
I think this will be a subject I keep coming back to.