Perhaps it could be possible to have the concept of the downvote expanded on the blockchain.
Add a set of flags to it, such as: plagiarism, irrelevant, spam, but keep things such as offensive out of it .. and have one of the flags be just "downvote".
If I disagree entirely or mostly with something I read here, sometimes I will downvote, but it seems funny that a) this is called flagging the post (I am not flagging anything, I just disagree with it and b) given enough downvotes by other users, the post will cease to be visible, which should not be the case if people are voting because they think the content is crap - but should arguably be the case if people are downvoting because it's spam, plagiarism, etc.