It doesn't have to be a trade-off between rationality and politeness. Maybe we could downvote both comments that are stupid and comments that are rude. (Polite but not smart comments could be ignored, and only insightful non-rude comments upvoted.)
I wonder who downvoted you.
I'd argue for more strict dealing of downvote moderation, a higher waterline, if you like; noninsightful posts get downvoted (and otherwise ignored, or if specifically wrong, corrected) and impolite posts also get down-voted and responded to with an explanation. Explanatory responses might need to be encouraged more, in order to permit the author to know why exactly their post is being downvoted, but I'm wary of encouraging the lesswrong community to become more of a politeness before reason community than it already has, and so many other communities out there have.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.