I think the big problem is in wanting the entire community to be the same way. We can chastise reddit or digg or 4chan or whoever for having group think, but it's the groupthink here to want "intelligent conversation". The problem is that anyone who doesn't adhere to this culture, or any internal culture, is then shunned by that culture. It's a side effect of scale that eventually the values and culture of the community becomes fragmented. No matter how good a site is at giving you the ability to filter based on your preference the simple knowledge that 'your community' has dissent in it, even if you don't see it, is enough enough to get most people complaining about the state of the community. It's more a humanity issue than a service issue.