I understand why even a pro-privacy group might think telemetry a good thing, but it's pretty heinous and shows questionable intent not to have it all sat behind a single on/off switch

The best is that Mozilla was very silent when they introduced it. They care about privacy just like Microsoft.

It would be nice to get something like the arkenfox user.js script here -- with explanations of what each configuration flag pertains to, the impacts it may have, all in an easy-to-copy script.

Just did a comparison. These are the ones not present in Arkenfox:

datareporting.healthreport.service.enabled

datareporting.sessions.current.clean

devtools.onboarding.telemetry.logged

toolkit.telemetry.hybridContent.enabled

toolkit.telemetry.prompted

toolkit.telemetry.rejected

toolkit.telemetry.reportingpolicy.firstRun

toolkit.telemetry.unifiedIsOptIn