After a couple of years of wanting this document, I finally felt up to writing "The Metaphor Rant".
The Metaphor Rant is a cogent argument that metaphors should rarely be used in a debate context, and should never be used in a domain that people do not clearly understand. I frequently find myself wanting to be able to link to this essay in online debate contexts, it's just that up until now, it didn't exist. Now it does.
I hope you find it stimulating.