If anything, link submissions or comment submissions should deduct karma so as to curb spammy (and possibly unsubstantiated) behavior. Of course this lends itself to issues of new users not being able to engage as much.
This is not a Nash equilibrium.
Everyone gets downvoted. It isn't interesting, and it doesn't matter.
In the real world there's a price to pay if you hit someone. Not on HN - hit people with downvotes and no comeback or explanation or cost.