I can't be bothered with reading much of what's been posted since this morning as it's just going over old ground.
But somebody asked what was the difference between him being on a dating site and meeting someone down the pub.
Somebody else has already mentioned high hit rates, access to women with children amongst others.
But other reasons I wanted to mention were:
Ability to hide any new relationship from the authorities. If a girlfriend is hidden from the rest of his social network, e.g. friends, family, workmates, neighbours then it's easier for it to be hidden from probation services who may need to protect/inform the women concerned.
It's easier for him to hide his identity (including the one he is supposed to be hiding under) which will make it harder for a woman to identify him as an offender and a potential danger, again because she will be cut off from the rest of his social network.
Meeting him online would also mean she was cut off from other warning signals like a lack of friends, other people in the local community who might have picked up that something was not right.
Also given the fact that he has assumed different personas in the past means he could well do it again and use it to trick his way into a woman's confidence. For example if he was to pose as a father ins responsible job like a teacher or nurse, which it is far, far easier to do online it may facilitate contact with children.
And to be honest, given his offending I would prefer if he wasn't online at all. Best way to ensure he's not accessing child porn.