@OP:
Oh dear, where to start:
- Trying to "win" some discussion (which includes "proving" something) is stupid and useless, unless one thinks of a discussion as some kind of sport. Yes, i know that a lot of people do that - they're all idiots, bored or have mental/emotional deficits that they need to compensate at the cost of others. You ask "Why discuss then?" Well, for example to mutually increase each others understanding - to mutually grow.
- There is no external judge. Every single participant in the discussing is a judge about his own worldview. Thus, it is impossible anyways to mindrape force someone else to accept something. The only thing that may be achievable is just pissing someone off enough that he/she's driven out of the discussion (those who consider discussion a sports game, equate this with "winning", even though the person that was driven away will probably think of the "winner" as an asshole and hasn't changed his/her "opinion" a bit - quite probably strengtened it instead)
- For each "judge", an opinion (which basically is just a synonym for "thesis") can of course be right, wrong, true and untrue.
So in summary: There is no "external judge" for ANYTHING. Neither for opinions or anything else. What happens simply is that people exchange information, and everyone involved rates the info according to what he thinks make sense. With this, i do NOT mean that everything is "subjective" (as in, there's a parallel world in everyone). All used arguments do of course have a general "correct" value - but since everyone can rate however he/she wants, there is no way to force how someone should rate - or in short: You cannot act in place of someone else. You are you, he is him.