in the limit of large stacks, long pondering times, and decisions jointly made by large organizations, people do actually behave rationally.

I still don't think so. To be a bit more precise, certainly people behave rationally sometimes and I will agree that things like long deliberations or joint decisions (given sufficient diversity of the deciding group) tend to increase the rationality. But I don't think that even in the limit assuming rationality is a "safe" or a "fine" assumption.

Example: international politics. Another example: organized religions.

I also think that in analyzing this issue there is the danger of constructing rational narratives post-factum via the claim of revealed preferences. Let's say entity A decides to do B. It's very tempting to say "Aha! It would be rational for A to decide to do B if A really wants X, therefore A wants X and behaves rationally". And certainly, that happens like that on a regular basis. However what also happens is that A really wants Y and decides to do B on non-rational grounds or just makes a mistake. In this case our analysis of A's rationality is false, but it's hard for us to detect that without knowing whether A really wants X or Y.