If you are talking about the abortion thread, I'd say that it was already derailed before people starting neg repping each other. At least, up to a certain point. I agree with Cach; the way you choose to use and respond to rep depends upon you as a person. I personally would never think about neg repping a person just out of spite or passive aggressiveness. I have given neg rep in the past and explained why I did so. In response, this person chose to confront me with it and it did spark a private discussion over the matter. I still talk to this person, so I'm assuming that he/she at least considered my point of view and I considered his/hers. Getting rid of a system because other people fail to get value out of it and abuse the system seems like an abdication of personal responsibility to me. I'd still like to be able to give neg rep if I really wanted to do so, which is rare. If used with integrity, I think neg rep is simply saying 'This is how I honestly feel about your position'. It is a statement of truth as I see it and not meant to be a condemnation of a person's character.
I do see merit in the fact that the neg rep system does not foster good communication in it self. In regards to the person I mentioned before, we switched the conversation over to PM. But then, positive rep doesn't foster good communication in it self either. Half the time, I don't even know why people are repping me. Should we get rid of it as well? Would we really lose anything of value if we got rid of it?
My answer should be fairly obvious with my recent posts. Assuming neg rep is disabled and nothing else changes, nobody loses anything and something which tends to get blown out of proportion is taken out of the equation. We're talking about the loss of a minuscule number of growth experiences for a gain in threads that don't get derailed and drama that isn't caused. That sounds like a win to me.