This is not true. `man brew` documents how to disable auto-updates.
> Why exactly is this kind of purist decision being imposed on users?
Because there's a lot of current debate about whether things being relicensed under the Commons Clause is "open source" or not and we'd rather lean on an established, well-documented authority on what that definition is. Additionally, part of our agreed membership of the Software Freedom Conservancy (who help us with a lot) involves ensuring our core formulae are open source software.
> So you're going to periodically make maintenance changes to my system without my permission. Goodie.
Again, `brew man` documents how to disable this.
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The complaint behind the individual complaints is "why doesn't Homebrew work the way I want it to". That's a reasonable complaint and there may be better tools for you to use rather than Homebrew but we're going to continue to build Homebrew to work in a way that works best for the majority of our users and avoids our (entirely voluntary) maintainers having to deal with the same issues again and again.