The problem is that not even Apple can guarantee it's not gonna be used for anything nefarious, since they won't have (and probably don't want!) access to the s

The problem is that not even Apple can guarantee it's not gonna be used for anything nefarious, since they won't have (and probably don't want!) access to the source of the PhotoDNA hashes to inspect them. Not only we have to blindly trust Apple, we also have to trust a (government?) institution that most of us had never heard about before.