Civility and topicality of a discussion isn't a measure of how mind-killed that discussion is. I personally very much doubt that I could have discussed Krugman rationally, had I entered the discussion, though I certainly would have been polite about it.

This has no consequence on whether politics is genuinely a mind-killer. I include this disclaimer because it has just occurred to me that (ironically) perhaps the "politics is a mind-killer" issue might be becoming LW's first really political issue, and prompt all the standard arguments-as-soldiers failures of rationality.