Mike Sanders makes an interesting observation on the Echo Chamber question:
It seems to me that an Echo Chamber is a group that ignores other opinions to their own detriment. I keep on thinking that David’s defense of the EC is rooted in an idea from Arnold Kling’s Downfall of the Annointed post in which he pointed out that some feel that trying to change people’s minds is a waste of time. Instead they just rally their supporters and wait for those who disagree to see the light
The essay he links is right on as well. Weinberger’s sticking to his guns on this issue, despite the fact that nobody agrees with him.