So what you're saying is that basically you have verification that the conversation you see is one that took place and that there are a fixed set of identities

So what you're saying is that basically you have verification that the conversation you see is one that took place and that there are a fixed set of identities (not people) who had that conversation? Can't we just schlep a merkle tree over the top of any forum software and get similar guarantees? And isn't this sort of false due the lack of convergence of the block chain over long partitioning events?