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It's hard to imagine how this could be enforced. What priest is going to be able to say with absolute certainty what the identity of the penitent was? Of course, he would be concerned that he might make a mistake. Maybe he had THOUGHT that it was John Smith confessing, who sounds a lot like Andrew Crabtree, but he couldn't be entirely certain which it was. Does he report both names? Then at least one would be a mistake. Maybe they're both mistakes! Then the real responsible party goes free and two innocent men are falsely accused!
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So they'd have to require that priests in Australia have a new system by which anyone confessing their sins would have to fill out an application to confess and a clerk or someone like a notary, would have to verify identity of the penitent before he would be allowed to enter the confessional, and the priest hearing the confession would have to have access to the verified information on the application while he's hearing the confession so he would be able to decide if what he hears rises to the level of his obligation to make a report. He might want to come out of the confessional to make a visual check on who the penitent was speaking to him. So they'd be prone to getting rid of the confessional screen that seems to hide the faces of penitent and priest. Does that encourage sinners to confess their sins?
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If it applies to child abuse, why stop there? If someone admits to murder, or bank robbery, or embezzlement or any other crime, why would the state NOT want to require the priest to report the information and attest to the identity of the admitted perpetrator?