You've got a point. As much as I think pedophiles should be executed, here in Michigan an 16 year old boy who has sex with his 16 year old girlfriend can end up on the Sexual Offender list. So can someone who got caught urinating behind a tree (indecent exposure). They need to have a specific "this person screwed a child and deserves to be publicly executed in the town square" list.
In my state, you can type in your city, and they'll list every sex offender, with a picture, and a notation as to the crime. So you have at least some idea. Of course, when you see the pictures of most of them, you'd probably keep your kids far away from them anyway.