As far as I can tell, bespin, you are approaching this as someone who deals with paedophiles and assesses how risky they are?
Whereas I think most of the posters here are considering things from the point of view of women who need to consider how to best keep potential threats away from kids & vulnerable people. We're just coming at it from different angles.
When you asked 'what would you do, lock him up?', you're completely misunderstanding. That's not the subject here. Nobody's talking about crime and punishment, only safeguarding.
What we would not do is give 'him' access to kids or vulnerable people - we're not police officers here, we're not talking about retribution, justice or law, we're purely talking about protection and safeguarding and how best to keep kids safe.
Anyone who may present a threat is kept away from vulnerable groups as much as possible. I would include people who willingly share information on their child rape fantasies in that category; I can't really imagine anyone who wouldn't.
When I'm considering safeguarding, I look for any potential threats and avoid if there are red flags. I don't and wouldn't, ever, give anybody the benefit of the doubt because there's no proof they're a criminal - in my view, trust has to be earned as a positive.
The criminal justice system - and, it seems, your work - works from the opposite point of view: innocent until proven guilty, quite rightly, that's an essential part of our justice system.
Safeguarding (as I understand it) has to pretty much work on the opposite premise - risky until proven safe.