A lot of the contention wasn't about the specifics of their plan, but rather how subtle changes could vastly expand the scope of their plan.
"this would only apply to photos sent to iCloud." for now, until scope creeps.
"this was only looking for previously known CSAM." for now, until scope creeps.
"using some sort of hash matching so photos you took yourself would not trigger the system." well this one is immediately concerning even within claimed scope because there ARE going to be false positives that apple records some database. Millions of iphone users are going to have a non-zero "possible childporn" score.
They are building an engine for iphone users to self-incriminate. If they rigidly hold the scope to only what they announced and never expand, it could be argued that this is a reasonable concession to fight CSAM. However, in making the announcement, they boldly stepped past their existing hard line in privacy (local device content is private and not surveilled by apple), so it seems naive to expect that this announcement reflects the eventual scope of this self-incrimination engine for the next decade of apple updates.