Is opt-out telemetry unethical ... depends. If you use it in a privacy preserving way no, if you spy on your Users, sell the data for money or advertising obviously it is unethical.
The hard truth is, nobody reads the manual. Opt in telemetry is often a minority, and you then work with niche data for a minority that influences your development in certain ways.
> if you spy on your Users
In my opinion, any data collection about me or my machines that occurs without my active informed consent is "spying". This is my fundamental problem with opt-out mechanisms. They do not indicate or imply that active consent was obtained.
Would that be enough for you?
In short, unless you're a Windows user there are so __very__ many ways to install software that aren't "Go to the project home page, download a generic install binary, run that binary with world-write permissions.". Aside from very small-time projects, I can't think of the last time I used an officially-maintained install script that I got from the project's servers to install something.