This is a good idea, but the definition of argument must be incredibly broad. Consciously or not, we don't want to end up censoring users that we don't agree with. Along the lines of the examples mentioned above ("ie "You're stupid!" and other rage-y, name-calling, simple statements), should clearly not be allowed, but that's, I think, about as far as we can go. If there is any doubt whatsoever, it should be allowed.
We decided that for some topics, such as topics related to politics, we will be requiring the opinions to contain at least one argument. Now, this isn't a strict rule. We won't be scanning the opinions to extract arguments from them. The general rule is that an OpiWiki opinion must add at least a bit to the discussion. If there are no arguments, but there's a bit that enriches the discussion (it can be something related to personal experience, some info, etc.), it's ok.
Why this rule? At OpiWiki we have some goals set. One of them is bringing the Internet discussion to a new level. We also want to grant the word "opinion" a better name. We believe that opinions like "he's the worst", "he's the best", or "he's an idiot", 1) lower the quality of our site and work against reaching our goals, and 2) don't add anything valuable to the discussion. Now, people who don't have anything more to say are not restricted from contributing their opinions, as we also have a voting system, and we believe that a vote is more meaningful in such cases.
You can learn more about the guidelines at opi.wiki/help/discussion#b.
If the topics chosen are VERY careful, I think it can work.
The issue is that it will discourage some from commenting at all, because they may not really want to get into a long issue (and are worried that specific statements might encourage responses they don't want to get into).
I think instead of "argument", which implies something more formally Aristotelian, it should be "a point of contribution". That could be a comparison, a metaphor, a poem, anything that wouldn't be a formal argument but (aims to) elucidate.
I still disagree... You should let your users decide for themselves whether or not an opinion is good or bad. You created a system that allows users to express their opinions on opinions, with the community accordance votings. By interfering with opinions, you remove the usefulness of the community accordance percentage. Because community accordance isn't just a stat. It's a tool. If people like or don't like an opinion, they will use their own judgement and rate the opinion +1 or -1. If an individual repeatedly gets bad opinion ratings on pratically everything, then, I believe you should monitorize this person, warn him/her if needed, see if the person is a troll and then use your moderation powers... Simply put, I think a moderator should not only moderate but also be moderate. :P
If you are too strict, people will simply go elsewhere even if they are not being moderated themselves. It's good to see a cop once in a while as you walk back home late at night, but it's not the same when there's a cop on every corner, right?
Besides... Let's say one day OpiWiki becomes very popular and you get hundreds of thousands of views everyday ( or maybe more ). You won't be able to keep up anyway. Not with tiny, insignificant comments such as "he's the worst". Even if you had an army of mods, you wouldn't be able to deal with them. You will have to focus on the extremes only.
I think we've all been idiots who couldn't form solid arguments at some point or another during our life! When I was 14, I was an idiot for sure. But, thanks to interaction with other people (including on the internet), I think I evolved and became a better person. I'm pretty sure it's the same for most people who grow up. Interaction is the key. If idiots are not confronted by smarter, wiser people, they will remain idiots... Give the poor folks a chance! ;)