I think I heard an excellent answer, somewhere, that suggested that upvotes/downvotes merely represent "I want more people to see this" or "I want less people to see this". This is implied in the system that will reorganize the posts such posts with higher scores will be put in a more conspicuous on the page.

As excellent as that answer is, however, I do wonder if it misses something. As much as we might prefer votes to have a consistent interpretation, I think this bends to the idea that the meaning of a vote on a post depends on the nature of the post. Sometimes it is a method of voting on whether the argument is sound, sometimes it is voting on whether you like the post, sometimes it voting on whether you like the poster, and sometimes it is voting on the rhetorical style of the post. Someone could even make a post saying "vote me down if you like this post", whereby votes are unparsably ambiguous.