your stance assumes we know the pedophile urges about this person. that the person has volunteered this information about himself
Are you assuming that people have not done so? Usually "volunteered" after they're caught, so not exactly volunteered, I'll grant you. But "volunteering" it beforehand has dire consequences.
obviously, this information is not going to be freely offered. you can imagine why. so we leave children alone with this person, because we don't know, and then we find out the hard way the person likes children sexually
The "imagine why" bit is revealing. I can also imagine a world where we would know, because the ramifications of admitting something like this - before any children are actually harmed - would be that they're afforded counseling if they want it, and they're not allowed to be alone with children; no more, no less. If other adults are around, as I said before - I have no problem with that, unless the person is openly lewd toward children - in which case I'm sure the other adults would take immediate steps to stop it.
So, in what way is our current state of affairs better than the imaginary one I just described?
As it is, there are few instances where you should ever leave your children alone with someone. One of those is if it's their relative. Sadly, most child abuse occurs by the child's relative. And it is tragic when it happens. However, I still can't help but feel that it's caused primarily because they are driven underground by shame and the fear of people knowing. If anyone knew, they would almost certainly have loved ones taken away and never be permitted to see them - for a very long time.
base human sexual desire is always there, and human will power is often weak. during that moment of weakness, alone, around a child, the inevitable happens
Looking at a picture is a seemingly victimless crime. Abusing a child results in a young individual who may be scarred for life. The difference between the two is not necessarily a simple matter of variable willpower.