Except the list of hashes is a black box. Today it's child porn, tomorrow it's anti-government or something similar. It's a slippery slope that's only going in one direction.
The only naiveté is self-inflicted by reading clickbait articles instead of how the system actually works. When people start worrying about Apple scanning for abstract subjects like "anti-government" they're worrying about some hypothetical system, not the one that's been built.
Your entire iPhone is a black box. If you don't trust Apple, there are so many points in the chain where they could backdoor you. The fact they are out in front of this is a good thing.
Also, I'm willing to sacrifice a tiny bit of privacy to stop child porn collections.
This[1] comment explains it very well. It just cements why I moved back to Linux on my laptop, and will be moving to something running open source software on my phone, and open hardware on all my devices.
As implemented, I agree with Apple