Uh, can't I choose not to have my private images scanned? I think that's still a choice, right?
It is, but it's perhaps incompatible with uploading your private images to a cloud service.
Of course. But the second you enable iCloud Photo Library and want to upload your private photos to Apple's servers than you need to comply with their Terms & Conditions.
Which includes them scanning your photos for CSAM.
And you can either choose between (a) someone having to see your photos or (b) relying on an automated but imperfect process. You have to pick one.