You might get lots of people to do it if there were two sets of arrows, something like signal/noise and agree/disagree. But that has been proposed before.
> Are there any downsides to this proposal?
None that I can see. In any case, many of us already do this.
> Of course, this means nothing without an official seal since PG already proclaimed that you should downvote disagreements.
I very much disagree with PG's famous statement. I wish he'd reconsider.