…surely if they have been abused they’d be even more intolerant of it than most…
Having had my brother work on a sex offenders wing in a large UK prison (seconded probation officer) and having talked to him about it: People that abuse are often in positions of trust and intimacy with the abused e.g. parents or relatives of the child. Being abused at a young age leads to an association of the abusing behaviour with love and affection in certain relationships. Basically, they can end up “wired” a bit wrong.
Then they repeat the cycle. I don’t think it’s as simple as that, I don’t agree with it, I don’t have a lot of sympathy for people that do it. However, the observation was made to me that most abusers were themselves abused. It wasn’t by an apologist or a sympathiser.