The best kind of correct.

With opt-in on an open-source project I get to choose to help contributing something back (telemetry data) to help the project.

Opt-out telemetry is not compatible with respect. It also adds an obstacle when I try to advocate the software to friends and coworkers. I have to warn them about it in advance, which is often where it ends because we’ve been burned in the past with other software adding extra things to their telemetry that weren’t there before, or changing the name of the environment variable that disables telemetry, or someone on the team does something that accidentally causes data to be transmitted unintentionally.