When negative karma would have been an issue is that, if it actually showed that a user has a negative karma on their profile on this misconduct like the way in the other forum.
Like the way it is here, if you, a user, are given a negative karma, what it will do is subtract the karma they already have; other users won't know a negative karma was given to a user.
In this kind of case, nothing is to worry about negative karma given to someone because it can't be undone, except you gave positive karma to counter it.