Right, by building in what amounts to a back door.

> One of your photos must be an exact match for photos already existing in the CSAM database, at which point a report is generated

IIRC, one of your photos must match a hash that exists in the database, not an exact match to an image itself. That's the means by which end-to-end encryption is evaded. That evasion is why I call it a back door.

Really, my entire problem with the scheme was that it took place on the device itself rather than in the iCloud. While all smartphones are surveillance devices already, making one as overtly a surveillance device like this sets a precedent that I think is exceedingly harmful.

No, I didn't miss that point at all. It's just orthogonal to my objection to the scheme. I object to the idea of formally making highly personal devices like your phone into ones that are spying on you. We have more than enough of that sort of thing informally. To make it official could only make things worse for everybody, Apple users and otherwise.

Since the whole thing was about photos being stored in the cloud, it would have been much less objectionable to put the scanning on the cloud side of things. At least that's actually someone else's computer and not someone using your own hardware against you.