I'm not sure that's true. A lot of people seem to have less of a problem with Apple scanning for CSAM and more of a problem that they're doing it on the phone (and looking for specific images, I guess?).
It’s the fact that the phone is scanning your images and relaying the results to Apple that’s the issue. If this feature were just an extension of existing on-device scanning and stayed on the device, perhaps informing the owner “Hey, it appears a few of your images may be CSAM. Would you like to review them?” then I don’t think people would be very upset.