I tend to this solution. The ability to decrease the payout of a post with a click should come with some form of cost, because otherwise it will always be used for downvoting different opinions. As far as I can tell, free downvotes are mainly being used by large stakeholders, because users with less SP fear retaliation actions (for a good reason, because nobody wants his account being destroyed).

But... We need an account (maybe provided by Steemit) with a huge amount of SP to be able to fight plagiarism, extreme cases of rewardpool-harming selfvotes and other kinds of serious abuse. As downvoting would then come with a cost, because the VP cannot be used for upvoting content and earning curation rewards, there won't be many Steemians willing to provide such a service. That's why Steemcleaners etc. upvoted their own posts and comments all the time.

Also we would need automated systems that detect potential abuse. Some kind of toolset that can help the community to find abusive actors easier. I would say, it should even be publicly available, so that it is fair for everyone and nobody gets downvoted for personal reasons.