Comment karma can provide constructive feedback to the comment's author. Often, but not always, a downvoted comment indicates that my point was not made clearly or that there were gratuitous remarks within the comment whose removal would improve the tone of the comment overall. Of course, sometimes comments are just downvoted because someone disagrees or because I intentionally was snarky.
Likewise, upvotes indicate that I have captured a portion of my audience's attention. Often this is because of some minor insight or extension of the conversation, though certainly on occasion I have been rewarded for snark.
In general, gamification is a viable system for influencing user behavior, and if only submissions were rewarded with karma, a great deal of undesirable behavior would be encouraged. The current system helps new HN'ers learn the ropes.
Likewise, upvotes indicate that I have captured a portion of my audience's attention. Often this is because of some minor insight or extension of the conversation, though certainly on occasion I have been rewarded for snark.
In general, gamification is a viable system for influencing user behavior, and if only submissions were rewarded with karma, a great deal of undesirable behavior would be encouraged. The current system helps new HN'ers learn the ropes.