Wow, that's remarkable. I can't fathom having the response of "why are you even doing this" instead of something more productive. It doesn't matter why they're doing it (and valid use cases are provided), negative numbers in a case statement should be supported regardless.
Edit: And finishing reading that thread now, Evan didn't even return once his question of "why" was answered. That's something else. I have no skin in this game, and people can run their projects as they see fit of course. But this behaviour doesn't make for a great community/ecosystem.
That's the appropriate response. You have to understand the problem to produce a solution. I don't read that as a negative response to the bug report. Just asking for more context.
The core team treat bug reports as insults: https://github.com/elm/compiler/issues/1773