If you're talking about photo library scanning, people would have to be saving the memes to their photo libraries, cloud syncing would have to be on, and they would have to save lots of them.
If you're talking about using the iMessage content scanning, this only applies to under-13 accounts, and it only notifies parents associated with the account.
If you are suggesting that Apple would be compelled to modify either of these to do something else, why would they bother with these, which are built with many constraints and multiple levels of failsafes, rather than just implement a new feature? Governments could ban end-to-end encrypted chat like iMessage. They could demand the next iOS update uploads your saved social media passwords to them. It's not very plausible that anyone would want to modify _these_ features rather than just implement something more direct and harder to evade.
Governments could make these demands at any point. They do not need to wait for this feature and then spring into action. The Chinese government did regarding where iCloud data is hosted for its citizens. The US government did regarding the San Bernardino iPhone case, and Apple fought back very publicly in court that any kind of modification of the OS was unacceptable.
The governments want them to do some thing preventing CSAM, so now they can match a perceptual hash--not content--to known images from an non-governmental organization. That is about the minimum invasive CSAM prevention anybody can do.
Can someone suggest an alternative CSAM prevention which is less intrusive?
It seems the alternative would be to continue to be a black opaque box, or NOT encrypt you photos and rumage through them.
If it's not explicitly listed in the end-to-end encryption section then assume Apple can access it.
So messages are opaque but photos are not?
Notice the absence of photos from the list that follows?
> So messages are opaque but photos are not?
Yes. Unless you use iCloud backup, in which case your key is included in the backup and technically even your messages could be accessed.