Suppose a selfvoter abusing plagiarism. He upvotes himself with 1000 rshares, and after that he receives 1000 rshares in downvotes. Let see what happens:

• the author receives 666 - 333 = 333 rshares.
• and curators receive 333 - 666 = -333 rshares... as this number is negative, it is changed to 0.

In conclusion, the plagiarism receives 333, and downvoters lose 333 for nothing (they put 1000 where only 666 where applied).
If downvoters want to give 0 to the author, they have to use 2000 rshares in downvotes (twice as much as in upvotes). So it will be more difficult to fight plagiarism, and bad content.