Suggestion: if you're going to start a new group blog, look at the group blogs that are most popular (like Huffington Post, Daily Kos, Bleacher Report, etc.) and think about copying them. My suspicion is that the LW "shame them in to maintaining quality" model sucks, and instead you're better off encouraging the production of lots of content and then building filter mechanisms on top of that.
I've been underwhelmed with the comments at Huffington Post. I used to think (partly as a result of being NPR junkie and partly from being exposed to left-wing self-image) that liberals were reliably intelligent. HP comments proved I was wrong.
This doesn't mean I think typical right-wing comments are better.
Edited to add: Two other places which gave me a good impression of left-wing intelligence: Making Light and Alas, a Blog.
To be fair, Huffington Post is hardly one thing. Are there blogs there anyone would recommend as having good commenting communities?
Various people (including Konkvistador who has been talking about it the most) have launched their blog More Right
"A group blog, More Right is a place to discuss the many things that are touched by politics that we prefer wouldn’t be, as well as right wing ideas in general. It grew out of the correspondences among like minded people in late 2012, who first began their journey studying the findings of modern cognitive science on the failings of human reasoning and ended it reading serious 19th century gentlemen denouncing democracy. Surveying modernity, we found cracks in its façade. Findings and seemingly correct ideas, carefully bolted down and hidden, met with disapproving stares and inarticulate denunciation when unearthed. This only whetted our appetites. Proceeding from the surface to the foundations, we found them lacking. This is reflected in the spirit of the site."