It's possible to move articles around. However, I believe that karma votes are saved as the value where they were originally given- and so if you write a main article, it gets downvoted to -4, and then moved to discussion, and upvoted (by different people) to 0, then the net karma change is (by my understanding) -36.

Which is also a disincentive to write great discussion posts then move them to main, since the votes aren't magnified.