Thanks for your message.
What you say about positive 'reps' may be true. My thinking is that it is like a pat on the back that could and should be done privately. Dissent, which is essentially what USMB is about, should be out in the open, mano-a-mano, presenting, defending and attacking where all can see. Plus, 'negs' are usually accompanied by snide and/or vicious remarks, showing the character of the sender that other posters don't discover.