Courts have determined that for this purpose the NCMEC is an agent of the government. NEMEC is 99% funded by the government and its ability to handle child porn is directly deprived from a explicit legislative carveout for them by name. What they do would be a felony for you or I to do. The fact that they are technically non-profit rather than an agency makes them significantly less accountable to the public. We cannot FOIA their communications, their composition isn't subject to public review, we cannot vote them out. And we have no way to tell what their database contains, nor is there any avenue for redress should we somehow learn of an inappropriate listing.
To the extent that you can say that they're not exactly a government agency, they absolutely have been deputized by the government.
> And we have no way to tell what their database contains, nor is there any avenue for redress should we somehow learn of an inappropriate listing.
Yes there is. It’s called legal liability. They are not immune to being held accountable for their actions just like any other non-profit. They may be immune from prosecution for possessing CSAM, but they don’t have any kind of immunity for damages they cause through their own actions.
So you would agree that Apple's use of private set intersection serves the purpose of shielding themselves and their data sources for the purposes of mitigating their legal liability from the harms created by false listings by concealing the content of the databases?
To the extent that you can say that they're not exactly a government agency, they absolutely have been deputized by the government.