A downvote is hardly punishment, it is just a community measure of the worth of a comment. From that point of view it is a learning experience, as you learn what is valuable to other people and what is not at all valuable.
If you can't handle correction, or the opinions of others, then Hacker News isn't for you. If you want to improve, learn more, and become a sharper, more attuned, internet citizen then this is the place to hone your skills.
When you measure something, like height, it's usually a uni-directional growth.
With karma here, it's bi-directional. So a downvote can actually take away your earnings so it's not that great of a measure because a polarizing comment could have +100 and -100 masked underneath a 0.
It is a learning experience. But just because it conditions people towards some behavior doesn't mean it's not also punishment. Punishment is a type of conditioning too, but it's also usually the less ideal method.
