The Steem Blue Paper describes the blockchain as a protocol that "enables people to earn the currency by using their brain (what can be called “Proof-of-Brain”)."

It's one thing if downvotes represented an expression of different points of view without negating the visibility of a user's "proof of brain." Instead, they are synonymous with a flag that can be employed by those with greater SP influence to blot out varying opinions, even when those disparate viewpoints are expressed in a clear and thoughtful manner and do not fit the description of content that is commonly cited for flags when one clicks on the flag button.