I think the problem is that buying upvotes is seen as a poor way to promote. Buying votes detracts from the way steem is supposed to work. The number one reason for downvoting a post is disagreement with reward. It's pretty easy to disagree with rewards when you are buying them. Is this post worth $15 or should some be returned to the reward pool for other creators? That's the real question everyone should ask when they are debating whether or not they should press that downvote button.

You may see buying votes as "promotion" but others see it as you and the bots raping the rewards pool. A downvote isn't an "attack", it's a vote on how rewards should be distributed, just as an upvote is.