I don't think the concern is scanning and uploading images. This could be justified in some cases. But once you open this door, it can easily expand to scan for other things. And people don't always read the notices for every update.
They have already proven that.
Unlike Google, they set up a system where no data hits Apple's server unless multiple images match known examples of kiddie porn.
But Google steps on your privacy in so many other ways, it's probably not worth defending this one technicality.
With Apple's system, no data hits their servers until multiple images match known examples of kiddie porn.
If there is a single false positive, Apple won't even know about it.
You can't provide data you never had, so Apple's system is much more private.