WTF?! Mackenzie Phillips

If you've been paying attention to popular culture lately you'll know that Mackenzie Phillips is writing a book. The most controversial subject matter is her incestuous relationship with her father John Phillips. Now I'm not going to delve too far into what the two of them had going on because I haven't purchased and read her book yet but her revelation sparked some heated debate.
Mackenzie was 19 when the alleged affair began and it was consensual so its not technically or legally defined as rape. Nevertheless its shameful and disgusting, especially on her father's behalf. First of all HE'S HER FATHER!!!! Regardless of how old she was, he was still her father.He has a certain responsibility to her. Secondly she was hooked on drugs so he was definitely taking advantage. But a lot of people say she seduced him. A lot of people say he wasn't at fault at all because they were both consenting adults. So what do you think? Is it okay to fuck your family members after your 18th birthday? Were they equally responsible for their actions? Do you think she's lying to sell books? Let me know.