In a zero-sum game in which a fixed amount of Steem is created every day, an upvote for one article is equivalent to downvoting every other article (of lower weight).
As a result, on the present platform, each upvote shouldn’t be merely viewed as a user’s appreciation for a given post, but rather as a statement signifying their preference for said content over all other. This is a glaring issue, as no curator should be able to pre-judge and lower access of content they haven’t seen to others on the website.

From my post on incentivized downvotes and a possible implementation. So in response to:

Which means your vote for one thing effective DOES negate a vote for something else.

I'll say that I agree, but you're also downvoting everything else on the platform. Also, the weight of that negative vote is nowhere near that of an upvote, so you create an imbalance that inflates the value of posts with higher visibility. Not a good thing.