Let's give him the benefit of the doubt for a minute and assume he is a decent human being and didn't know the extent of his friend's depravity (I know, I know).
This cease and desist stuff... playing mental gymnastics, what are you accomplishing that makes you feel morally in the right?
Are you "protecting your friend"... who has shown himself to be a danger to minors?
Are you "protecting your brand and livelihood"... at the cost of placing kids in danger while protecting your friend?
Are you "protecting the privacy" of the existing victims... despite their being totally anonymous, and your actions might lead to future minors being placed in danger by silencing it?
Do you "want your friend to get help"... even though you have very little control over that, and know he's already used your name and platform to secure access to victims in the past?
These are not the actions of a betrayed man who feels guilt and regret for his part in what happened and wants to prevent it in the future. In the most charitable stance, he's completely indifferent to what actually happened and wants to silence it for personal expediency.