> "Opt-out telemetry" creates precisely the scenario I describe, where ... no one knows ... why they're opting out.

Telemetry doesn't tell you why users do anything. They would have to ask, which doesn't require telemetry. There used to be a form for submitting feedback.

> How could Mozilla respect the needs of users who opt-out of Mozilla knowing they, and their needs, exist at all?

Because of the values and principles that Mozilla used to share with its users, the principles that underpinned the first implemenation of Firefox Sync and were completely abandoned in the current implementation.

I trusted Mozilla because they didn't require our trust. They understood this principle and designed their systems in accordance with it.