> While today it has been purpose-built for CSAM, and it can be deactivated simply by shutting off iCloud Photo Library syncing, it still feels like a line has been crossed
Two simple facts:
(1) The system, as described today, isn't any more invasive then the existing CSAM scanning technologies that exist on all major cloud storage systems (arguably it's less invasive - no external systems look at your photos unless your phone flags enough of your photos as CSAM, which brings it to a manual review stage)
(2) Auto-updating root-level proprietary software can be updated to any level of invasion of privacy at any time for any reason the provider wishes. We aren't any closer to full-invasion-of-privacy with iPhone than we were before; it is and always has been one single update away. In fact, we don't know if it's already there on iPhone or any other proprietary system such as Windows, Chromebook, etc. Who knows what backdoors exist on these systems?
If you truly believe that you need full control and a system you fully trust, don't get a device that runs proprietary software. If you're okay with a device that isn't fully trustworthy, but appears to be benevolent, then iPhone isn't any worse than it was a month ago.
Until there's evidence otherwise, iPhone will continue to be as trustworthy as any other proprietary closed-source system. If you need more than that, please contribute to projects that aim to produce a modern, functional FOSS smartphone.