The more I'm looking at the system, I see that downvotes are just fight-provoking feature. In my personal opinion, I don't need the -1 - I can easily spot troll, stupid person or someone who I just dislike. I also have mental 'ignore' function, so I don't really need the -1. I can't agree that expressing opinion should be punished.
On the other hand, if we continue to have the +1, it drives a more positive attitude towards the whole forum and discussion thing. Making a good argument on a certain point should be enough to convince the person. Yet, if he's a stub, there's not much point in talking to him. When was the last time you won an argument with the radio?