Thanks! I'm glad we asked. Felt uneasy either way. Also would appreciate any pointers, perhaps someone you know has written on ethics of it?
The big one with telemetry, is unintended side effects due to correlation and deanonymisation - which is actually dead hard to anticipate - very easy to get wrong like rolling your own cryptography :)
The other, around consent and defaults, is that even if your telemetry is perfectly anonymous, benign and beneficial to the end user, you may trigger a security alert and over-zealous investigation and reporting. This can have a massive impact on your reputation, as happened to Audacity. It's really not worth taking the risk.
Hope that helps.
[0] https://www.emerald.com/insight/content/doi/10.1108/S2398-60...
This level of incompetence borders on malice, regardless of intent.