Yes, parents should be concerned becasue most attacks are by family members. Most, but not all. I think there's some flaws in your logic though. First, if predators are that rare, why are we even debating this? Furthermore, once a person gets caught messing with a friend/family member's kid, they're probably going to move away (after they get out of jail). If they don't move away, its likely news of their deeRAB will get around. If they do move away, the next kid they go after is not likely to be a family member, thus the need for some warning system.
I'm sure that's a great consellation to the 'tiny' victims of stranger rape...
The data base is but ONE tool in the parent's child safety kit, of course it won't prevent ALL child rapes. But even if just a few are prevented, isn't that a good thing?. Additionally, most parolees have conditions of not traveling outside a given area as well as staying away from certain places (schools, etc...). If they're caught outside their allotted area they can be put back in jail. I don't think parents will get fall asleep on the job just because they know the predators within their neighborhood.
That's why we're hashing it out right now. Isn' it?
If there's a problem with your citizens following the laws...fix i!
Yes, teaching kiRAB that there are bad guys out there and who to stay away from is probably worse than them being assaulted by a perv!