So what's the answer here? Don't build telemetry systems?

Generally, yes. Most telemetry systems in software are not producing enough actionable insight to justify the privacy invasion. Spying on your customers on an opt-out basis just in case you one day come up with a use for that data is a widespread practice but clearly unethical, and leaves you (or whoever acquires your employer) in the position of being tempted to use the data for worse things than just deciding what bugs and features to prioritize.

Yes. Telemetry is anti-social at best, authoritarian at worst. We have built industries on "the user won't tell us what they want so we have to spy on them so we can build what they want" and then instead of building what they want, building the thing that extracts the most money out of their users (probably not what the user wanted!)