So let's take being kidnapped out of the equation. A four year old typically has little experience in making important decisions. My six year old would probably panic if she got separated from us in a place as big as AK, and she wouldn't know the park well enough to be able to navigate it. What if the child ended up trying to find a cast member to help but wandered into an unsafe area. There are places that are off-limits b/c they are dangerous, and small children might try to get into those areas b/c they wouldn't be as crowded as others. Yes - it would be stupid for the child to do it, but a terrified 4 yr old alone in a strange place with a bunch of people he or she doesn't know should be pretty freaked out (after all we educate them not to talk to strangers - strangers are bad). I'd say there are many reasons to panic if your young child goes missing, and a cast member who doesn't stop to help you search is certainly lax in judgement. The CM needs to be on it in a heartbeat b/c let's face it, not only is it the right thing to do, but a kid who wanders off and gets hurt while mom is waiting patiently by the CM is a lawsuit waiting to happen.
Also, there may never have been a child kidnapped from a park, but there is always a first time for everything. We were staying at AKL when the Swan incident happened, and every parent I saw was talking about it. We felt safe to let our guard down b/c of where we were - Disney. The incident could have been at any pool - at any resort - at any park. It was a huge reality check to dh and I. We try to keep the girls in sight at all times b/c not even the happiest place on earth is 100% safe. I just pray it never happens to us.