Opening up blog comments on a relatively popular website doesn't necessarily encourage discussion. See Youtube, TechCrunch, or really any others. Popular bloggers like Andrew Sullivan have shut down their comments precisely because they prefer a more personal conversation via email rather than the anonymous name calling and hate spewed in your average comment section.

I happen to think there is a place for comments. But I assume by default that most comment sections are open first, then closed because of the vitriol. That stuff takes a real emotional toll over time.