Free downvotes should lead to an improvement in quality and reduce plagiarism and spam. I'm all for it!

I think I have to agree here. If you have to make a choice to give an upvote or a downvote on the same power, it almost seems as though you're having to choose between a negative or a positive action, giving the idea of downvoting a seemingly negative connotation as opposed to a regulatory function. It also seems fair in the sense that you will be able to take action in flagging bad posts that are clearly horrible, without having it cost you. If you wish to moderate beyond your scope, at that point, it begins to cost you. Each day you are given a fresh set of moderation powers to combat negative content. Seems fair enough to me!