Ahh! It's a slipperly slope!
While maybe a bit skewed in the context of a discussion about kiddie touchers, I think Zing's general point about police entrapment is totally valid. If we move the context to a poor urban neighborhood and change the bait to an unlocked car waiting to be stolen or stripped, how would you feel about it then?
I mean, sure stealing is wrong, but would anyone have stolen the car if the police hadn't put it there? And how come those types of stings never happen in rich neighborhoods? Wouldn't it be a better use of public funds to promote education and economic opportunities in those poor areas than to entice the citizens to commit crimes, possibly leading to extensive jail time at further expense to tax payers?
If you zoom out a little bit on this, you can start asking a whole lot of other questions. With the booming private prison industry we have today, I'd kind of like to know how many crimes are actually police-induced.
The difference with a lot of pedo undercover work is that if a child molester stumbles upon a cop acting as one, chances are they were looking for a kid. In the case of online stuff, I don't think cops generally email an online predator about hooking up with a 12 year old; they just act like a 12 year old in chat rooms and what not. If you're in a chat room of 12 year olds, and a predator contacts you, there's no entrapment.
Extend that to the car example if possible: the unlocked car was parked in the middle of a parking lot, only reason a car thief would steal it is if they were walking through the parking lot looking for a car to steal.