"No one opts in" aside, any opt-in metrics you do collect tend to be skewed towards how the people who opt in, use the product. Anyone serious about making product decisions using opt-in metrics should be aware of this bias.
This could be solved by a lot of transperancy about what collected telemetry is saying. A user can then check if the users that opted-in to telemetry are representative of his own use cases and thus make an informed decision if he should opt-in as well (if he's not well represented). Telemtry is a lot like voting.
The vast majority of people will not read about the collected telemetry, even fewer will read it and then make a decision to opt-in.The telemetry is optimizing for the vast majority, not the loud minority, hence opt-out works better in order to cater to a larger group of users. Your voting analogy is really bad.
With that said, I don't really like telemetry and will turn it off.