Some social media sites with karma scores actually encourage one to ask why a post/comment is being downvoted. I guess they're in the minority, though. I don't know the consensus on Hacker News.
The HN guidelines say to "resist complaining" about downvotes. (I guess it's open to interpretation whether "asking about downvotes" falls under the same reasoning.)
All that is off topic. I think we should maybe change the guideline to say: "Please don't comment about being downvoted. It does no good and makes for boring reading."
