Imagine an attack where bots send suspicious photos to every phone in the planet.
After Cook and co have this happened, they'll rethink this program real quick.
2021 swatting
For the child iMessage system it would notify the parents, not law enforcement.
It's nothing like swatting
The whole point of this change is that they will scan content "before" it hits iCloud. (the verbage says "before" as if there is going to certainly be an intent that it goes to iCloud but that's not a given at all, sounds like Apples marketing speak to "assume the sale" so to say).
CSAM scanning of photos uploaded iCloud photos has already been in place for quite some time.