If one really thinks that downvoting should be encouraged than it doesn't make sense to make every downvote cost 1 Rep. In that case they could simply remove the Rep cost.

That will increase the number of downvotes but it might produce a more hostile environment. It might reduce the number of newbies around who will get downvoted. Experts however might be encouraged when they are able to down vote stuffs they consider to be wrong without cost.

It think the more hostile environment would be worth the cost because at the end of the day the average quality matters more than quantity.