This is what end-to-end encryption is for. A properly designed system shouldn’t allow anyone but the user to see the data, not even those who created the system.

In your model you need to question who decides what “good” is. Protecting children is always the way they try to get public support, as it is seen as a universal good. Once the practices have been established, what else is “good” and who decides?

Suppression of political messages the company doesn’t agree with? Something that Verizon has done and T-Mobile seems to still being doing in SMS. How about scanning for copy-written material? I can see it now, a 5th grader getting a summons for a picture of a painting they used in a book report. How about parents getting flagged for taking picture of their babies? Or a woman who needs an abortion, but lives in a state where it’s not allowed… someone might thinks it’s “good” to stop that from happening and arrest her for trying.

Searching someone’s phone or storage is no different than searching through their home. We have protections against random and unwarranted searches for a reason.