UX Movement have an article about how the thumbs up & down buttons you see on websites are dumbing users down by reducing the quality of the feedback that is provided.
YouTube used to have a star rating system. They found that the vast majority of ratings were five stars, and that very few people used the options between 1 and 5. So they switched to a simple ‘up or down’ system.
The problem with primitive systems like this, is that you’re reducing the overall quality of the comments to an equally primitive nature. You can see this for yourself on any YouTube video.
However, YouTube isn’t necessarily trying to build a community. If ‘drive-by’ comments are all they need, then a basic interface like this is fine. If you’re looking for a better quality of discussion, such as what you see in Slashdot, then you need to offer people a better interface. Slashdot allows people to only see highly-rated comments (or more if they wish), and for people to moderate comments with a wide variety of options.
Slashdot have a highly motivated audience though, one that most other sites can only dream about. People get rewarded for their contributions with ‘karma’ and a higher reputation, and other sites, such as Digg, have a system for rewarding frequent posters as well.
By allowing low quality comments to be visible, sites run the risk of damaging their brand. I would like to believe that the readers of Stuff.co.nz are intelligent and well informed, but if I read the comments on articles, I am often embarrassed to find that the readers of Stuff appear to be mostly trolls and rednecks.
So now the question is, how can we build a community and encourage high quality discussions? Smashing Magazine has a summary of different options for this, but the answer depends on the drivers of your audience.
If Stuff and NZ Herald implemented a proper discussion system, then the low-ranked (and presumably low value) comments would be hidden, and a decent threading system would allow people to engage in a conversation about the topic. This would encourage people who would like to contribute to do so, but to not be closely associated with the idiots in the community.
The quality of the comments that are left will be a direct result of the level of sophistication that your site provides, and the community feel (if any) will evolve from that.