Its a lot more honest than voting for retention. No singer can be retained because of a cult following. Only at the last, when it is down to the last two, should the vote be for the one you want to be the idol. The rest should be negative votes. Weakest link type.
All the cult followings (people who will end up buying CDs) is switch from voting for their choice to voting to eliminate whoever they perceive as the biggest threat to their choice...the net result wouldn't change that much.