The idiots would generally receive no or hardly any reputation points. Thats the idea of a reputation system
. Besides, as T-nex pointed out. Moderators could have the power to remove reputation or it could be linked to the infraction system where one loses a set number of rep points for each infraction given.
And btw, the current stars, the post counting and the user titles are also funny little things to make the forum experience a bit more fun. A reputation system, IMO, would be a nice addition to that list.