[Zak]

I have a hard time imagining any significant number of people objecting based on the sender's privacy. An adult sending explicit images to a child is a crime in most jurisdictions. A child doing it with a recipient under 13 is a concerning behavior the parents need to address.

Notifying the parents even requires that the child acknowledge that's what's going to happen.

[fwip]

Presumably they were worried about misclassified images, or images sent by other kids.

[themaninthedark]

The above proposed system could get ugly...

Family A enables system.

Kid B sends dick pic to Kid A.

Kid A decides to view it, Apple notifies and makes it viewable to Parents A.

Parents A are now guilty of possessing CSAM. (Distributed by Apple for extra fun)