could not vote? ofc they can vote, just not on themselves.
if the party's are a bit uqual you'll just miss 25% ( or 20? are there 4 or 5 party's? xD) IF everyone would vote on 1

But now you just waste good votes. becaus 50% is on themselves.. making it unfair
even if the other party has a kick ass good interview or Haiku it wouldnt mather becaus that vote go's the your own party.
its greedy and corrupted