We absolutely all do unknowingly. I have discovered not one, but two child sexual offenders in my very close immediate family (MIL's partner and my stepfather). Both of them are a bit odd/eccentric, but neither would give you paedo vibes if you met them at the pub. One has been to prison for 3 years and the other pled guilty and had a community order and was in a sexual offenders rehabilitation programme in the community for several years after.
Knowingly would I have someone I knew/believed to be a rapist/abuser in my life? No, not if I can help it. If it was a work colleague, I wouldn't have much choice, but in my personal life, nope, absolutely not. Dh and I have cut them both out of our lives and our dc's lives. I am NC with my mum. We have limited contact with MIL. I would have preferred none because it goes against my values, but she believes he was wrongly convicted 🙄and while that's ridiculous (he wasn't), it's a bit different to my mum, who knows that my stepfather did was he was accused of/pled guilty to, but thinks it's okay because it could have been worse. 😖
But the reality is, that despite what most people on MN will say, the vast majority of people with a rapist/abuser in their lives will carry on as if everything is absolutely fine. With the exception of the children who were abused, no one has cut contact with these men in my family except for us - literally everyone is absolutely fine with it. Or at least fine enough that it's easier just to not talk about it and pretend it never happened. The only people who have been cut out of the family are the children who were abused and us for speaking up about it.
So while I think there are some strong, principled folks who would cut ties, like we have, most people will not. Because an abstract 'rapist' or 'child abuser' is a scary thing, but Uncle Bob who seems kindly enough, except for this one bad thing, is not as scary and most people don't want to rock the boat or cause drama or be cut out of Christmas lunch or the will. So they keep their heads down and don't say or do anything that will cause a stir.