The problem is that it isn't meaningless. I was in the middle of a rather interesting ethical discussion, and many of my posts that I had just made went from 0 to -1, potentially dropping off of the radar of other readers. All it takes is two users colluding (or one user with an additional sock account) to effectively shut down someone else's entire voice.

If a post goes from 4 to 3, that isn't a big deal, but if it drops below the minimum display threshold before anyone gets a chance to read it, the entire flow of conversation gets disrupted.