They are paedophiles (a mental disorder) which have sucumbed to the temptation and become child abusers (a criminal act), or people seeking power/control over somebody else (so not all child abusers are paedophiles).
There are online communities of paedophiles in which they support each other to not become child abusers.
There are online communities of paedophiles in which they justify abusing children. They rationalize it, making other paedophiles become child abusers.
Paedophiles demonisation by the general population makes them hide instead of seeking help. Sooner or later they end up in one of those online communities, whether it's of the first of second type is basically luck.
In some places things are so crazy that doctors are legally required to report paedophiles to the police, making it impossible for those paedophiles to seek medical help.
Here you have the story of a former paedophile who was treated by medical profesionals and is now happily married (this one was only attracted to children, some paedophiles can be attracted to both adults and children): https://www.bbc.co.uk/bbcthree...
According to https://www.bbc.com/news/uk-41... (where a younger paedophile tells his story) "There's some debate about the numbers, but it's estimated that between 1% and 5% of men have some form of sexual interest in children". One study, by Professor Tamara Turner-Moore at Leeds Beckett University, suggests up to 10% of men have sexual thoughts about children at some stage in their lives. So paedophilia is relativelly common, but as a society we have branded it repulsive so clearly that even paedophiles usually don't act on their feelings (and you would not know if your best friend is a paedophile). But being so many, and without access to help, quite a few are going to become child abusers.
There _are_ people trying to stop potential future paedophile child abusers from acting by helping them before the fact: https://www.bbc.co.uk/news/mag...
You have to take care in checking how you treat that people, though. You can even end up making it MORE likely they will reoffend: https://www.bbc.co.uk/news/uk-... if you get it wrong.
There are also some which are having an impressive success https://www.bbc.co.uk/news/mag...: "According to Saunders, their re-offending rate is surprisingly low - 6% compared with 50% for the general prison population"
The BBC (so not some kind of pro-children-rape website) has more articles about the topic, e.g. https://www.bbc.co.uk/news/mag..., https://www.bbc.co.uk/news/uk-....