> Once the feature exists your local data might become accessible to a government warrant, which would make the iPhone the opposite of a privacy oriented device

Why does that dystopia require on device scanning? Why couldn't they just do it with an OS update today? It's not a reasonably slippery slope, given the actual mechanics of how the CSAM system was designed (perceptual image hashes, not access to arbitrary files)

> There's no reason to use customer's CPU/battery against them.

That's the better argument, but still not super strong. On-device scanning means you know and can verify what hashes are being scanned for, who is providing them, and when they change. Cloud scanning is a complete black box. None of us would know if Google was doing ad-hoc scans of particular users' photos at the behest of random LEOs.