I don’t think the scare is warranted.
This really is a narrowly targeted solution that only works with image collections, and requires two factors to verify, and two organizations to cooperate, one of which is Apple who has unequivocally staked their reputation on it not being used for other purposes, and the other is NCMEC which is a non-profit staffed with people dedicated to preventing child abuse.
People who are equating this with a general purpose hashing or file scanning mechanism are just wrong at best.
It’s not like the no-fly list at all.
Like with the TSA and the no-fly list. Civil liberties groups said it was going to be abused, and they said so well before any actual abuse had occurred. But they weren't overreacting, and they weren't exaggerating. They were right. Senator Ted Kennedy even wound up on that list at one point.