How are you going to determine a false positive?
If anyone saved pictures from dating apps, hookup apps, *-gone-wild subreddits, sexts, or anything else - and unlike Apple, we're not going to pretend that humans aren't sexual and don't save sexy pics, girls included; they are sexual, and they DO save sexy pics on their phones - then any of those pics could get flagged by some AI/ML algorithm.
It seems safe to presume that your privacy will then be violated first by those Apple is having check this stuff (and one would further doubt that they'll stop at looking at *just* the image that triggered the algorithm).
Then violated again when Apple's minions report you, and police/agents of the government pour over all of your media.
Then violated again when they decide to charge you with some crime, possibly with a highly subjective component about "appears to be" or whatever, and that arrest/charge shows up... wherever - news media, public records, and so on. (Of course not everyone will be charged; it's highly convenient to only charge the wrong kind of people with certain crimes, or when you want to "throw the book" at someone)
While (for now) it's incumbent upon the government to prove "beyond a reasonable doubt", as we know damn well the mere *accusation* of impropriety regarding sex-anything is enough to damn people in the court of public opinion. ...and if you trust a "jury of your peers" to consistently take a completely legal picture of an adult who happened to do something as simple as shave off his or her body hair and actually, correctly apply "beyond a reasonable doubt" to it when they decide things behind closed doors? Well, I have not one but TWO bridges to sell you.
It's one thing if you can tie an image back to, say, a porn site - and we're talking exact image (file hash) or very heavily image-matched version of it - we know that cloud storage can/will/offer re-compression of images to save space, but in order to actually be "safe", would we all have to become the equivalent of 18 USC 2257 record-keepers lest we get accused of something which we're unable to disprove?
Overall? Well, that was a nice republic (royal) you had there.