@tomrittervg It doesn't matter how useful you think it is. It's still unethical and wrong.
I could go through your examples of "Concrete wins from Firefox Telemetry" one by one and detail how each should and could have happened just as smoothly without telemetry, using normal, ethical means like paid QA, voluntary reporting by power-user early-adopters, etc.
But I think this misses the point. You don't get to decide that having telemetry on-by-default (even with an way to opt-out) is acceptable just because you think you think it produced immensely beneficial results.