The problem with this is it makes every submission into a karma game. If submitting costs karma, it will cause more people to think "will this earn enough points?" before submitting links.

... but that's not what you want people to think. You want them to think "is this interesting and on-topic for HN?" They're not the same question, as much as the former tries to approximate the latter.

If people focus too much on points, you're likely to get more groupthink and more industry buzz (since that stuff always gets a gazillion upvotes) instead of interesting articles.

Certainly, people think about link karma already, but I think this would make it worse. Creating a cost will cause even people who don't think about karma to think about it, even for just a moment -- which is probably not what you want.