There is truth to this sentiment, but you should keep in mind results like this one by Scott Aaronson, that the amount of info that people actually have to transmit is independent of the amount of evidence that they have (even given computational limitations).

The point I wanted to make was that AFAIK there is currently no practical method for two humans to reliably reach agreement on some topic besides exchanging all the evidence they have, even if they trust each other to be as rational as humanly possible. The result by Scott Aaronson may be of theoretical interest (and maybe even of practical use by future AIs that can perform exact computations with the information in their minds), but seem to have no relevance to humans faced with real-world (i.e., as opposed to toy examples) disagreements.

I don’t think the failure to have common knowledge is much of a vice, either of me or my interlocutor. It’s just a really hard condition.

I don't understand this. Can you expand?