Prior to this when a government tapped Apple on the shoulder asking to scan for what they (the government) deem illicit material, Apple could have feasibly say "we cannot do this, the technology does not exist".
Now the box is open, the technology does exist, publicly and on the record - Now we are but a national security letter, or a court order with an attached super-injunction, away from our computers and phones ratting us out for thought crime, government critique and embarrassing the establishment. At first it's the photos, but what about messages and browsing history or the legion other things that people use their devices for, when do they follow?
CSAM is beyond abhorrent, morally reprehensible and absolutely should be stopped. This is not in question. And I have no reason to doubt that there is sincerity in their goal to reduce and eliminate it from Apple's perspective.
But they have root; this system and it's implementation is a fundamental betrayal of the implicit trust that their users have placed in them (however foolish it was, in hindsight). It just is not possible to regain that trust now that it is gone, when the level of control is so one sided and the systems involved are so opaque.