The pyramid of debate is good, but we probably need other guidelines as well.
I think it would be helpful to have a list, always one click away (in the footer), so we could point out specifically why/how people are pulling the tone down.
We don't have to reinvent the wheel; LessWrong and Wikipedia have laid a lot of the groundwork here.
Wikipedia has aims (see Five Pillars in the link above), and these shape the policies.
Parallel to this is a means of creating and editing the guidelines. In a word: governance. Wikipedia does this by consensus. Most sites do it by monarchy. Another option would be to vote in a board of governors to rule on decisions where consensus is not clear.