I know this is a huge thread, and I haven't read every post -- but, I just need to post my two cents. The CHILD PORN scanner is absolutely no big deal. It's NOT going to flag the photo of your kid in their first bath. It's NOT going to flag the photo your kid took of themselves nekkid. It's NOT going to flag literally any "normal" photo parents take of their kids -- and it won't even flag photos 17 year olds take of themselves to share.
It *will* flag photos that are KNOWN TO BE CHILD PORN and are traded on the dark underbelly of the internet. If you have CHILD PORN ON YOUR PHONE you need help; and hopefully the Apple scanner will find you and get you the help you need.
If this tech existed years ago, Josh Duggar wouldn't have molested his sisters for anywhere near as long as he did.
Bottom line -- if you're WORRIED about Apple finding CHILD PORN on your phone, maybe you shouldn't have ILLEGAL CHILD PORN on your phone. In other news, water is wet, and illegal **** is illegal.