If you're operating in an environment like the internet where you can more or less guarantee that there will be one comment based on the the worst possible interpretation of what you said, being charitable in advance just makes things worse for you. You're playing "cooperate" with an endless stream of "defectors". Trolling has always been "defect" in this environment.
Hence the value in having more closed environments for discussion. HN is open enough that people can make throwaway accounts and use them for valid points, and closed enough that the more obvious trolls get downvote-hammered quickly.