[supertrope]

It wouldn't stop at CSAM. Along side it in urgency of appeal to fear is counter-terrorism* . Next would be drug dealing, threats of violence. Then copyright infringement. And finally Amber Alerts and silver alerts. A backdoor or warrant-less search for one category is a backdoor for all. The point is for government power to trump privacy.

*The definition of terrorism depends on your jurisdiction.

[AlexandrB]

While the on-device CSAM scanning was a huge overreach I'm not sure how you could leverage that system for things like Amber/silver alerts or threats of violence. It's not really backdoor, more of a snitch system.