Many points that are both new and good. Like prase, and like a selection of other fine LW-ers with whom I hope to be agreeing soon, I think your post is awesome :)

One root of the agreement/disagreement asymmetry is perhaps that many of us aspiring rationalists are intellectual show-offs, and we want our points to show everyone how smart we are. Status feels zero-sum, as though one gains smart-points from poking holes in others' claims and loses smart-points from affirming others' good ideas. Maybe we should brainstorm some schemas for expressing agreement while adding intellectual content and showing our own smarts, like "I think your point on slide 14 is awesome. And I bet it can be extended to new context __", or "I love the analogy you made on page 5; now that I read it, I see how to take my own research farther..."

Related: maybe we feel self-conscious about speaking if we don't have anything "new" to add to the conversation, and we don't notice "I, too, agree" as something new. One approach here would be to voice, not just agreement, but the analysis that's going into each individual's agreement, e.g. "I agree; that sounds just like my own experience trying to get an atheists club started", or "I'm adopting these beliefs now, because I trust Eliezer's judgment here, but I have little confirming evidence of my own, so don't double-count my agreement as new evidence". Voicing the causal structure of our agreement would:

• Give us practice seeing how others navigate evidence and Aumann-type issues;
• Expose us to others' evidence;
• Guard against information cascades (assuming honesty in those participating);
• Let us affirm our identities as smart rationalists, while we express agreement. :)