Perhaps downvoting a post should have a negative effect on the downvoter.
We had that, flags cost upvote mana in the original design, but the one I won't name was soooo abusive that the code was changed to give free flags so that guy could get run off the platform.
I wouldn't oppose bringing that original design back, or adjusting its freeness to one flag a day, the amount of abuse is much less now, afaict.