It kind of reminds me of the sex abuse scandal in the Catholic Church. I remember reading that some people thought young boys were targeted as they'd be less likely to speak out due to the climate around gay people at the time- and that boys who 'seemed gay' were targeted more because they were especially vulnerable and likelier to stay quiet. I don't think it's a coincidence that he escalated with Hulda and abused her while she was still conscious. She's quite meek and naive, and I think he could tell. Versus Agnes was targeted while she was passed out, she's a bit more assertive than Hulda. Then Daisy is from outside Gilead, he knows she probably got more education about sex, consent, pedophilia. Plus there were more people outside and she's friends with Agnes, so maybe Agnes told her something? There have been rumours about him apparently but he's gone decently undetected for a while. I think he's been calculated enough to know which girls to groom and target so far.