“There is no society in human history that ever suffered because its people became too reasonable” -Sam Harris
Maybe it's people or maybe it's suffering, but put them together and I think you notice: people's suffering is not exactly additive. So what does it mean for a society to suffer? Is it that more people are generally unhappy? Or that the unhappy are unhappier? Or that some calamity befalls them? Or, say, what do we make of North Koreans, who by any objective means are suffering, yet seem almost eerily happy? What I'm trying to say is that it's not so easy to think of many different examples of societies suffering. The only ones I can think of involve wars, genocides, and economic collapse.
So what this is saying, to me, is no society ever got into a war, was a victim of genocide, or had economic collapse from people becoming too reasonable. This is a little non-sensical, but might be true. That is, it might be true depending on how you define reasonableness with respect to hindsight - because reasonableness of an action or point of view has something to do with its outcome. To take a hypothetical example, say the people of country A decide that it's unreasonable to expend too much money on national defense, and vote for a party that wants to cut national defense. In some cases that is a reasonable thing to do. But, say, then, country A gets invaded by its neighbour, country B, and the people suffer. Then, because it led to a bad outcome, this clearly wasn't a reasonable action on the part of the voters of A. But of course, had they not been invaded, then it would have been reasonable, and wouldn't have led to suffering. So, in effect, for a large class of definitions of "reasonable", this statement is a tautology.
It's even worse than that. For other definitions of reasonable, this statement is obviously false. Take, say the Great Depression. People acting reasonably - taking their money out of unsteady banks, and saving it rather than spending it - caused a great deal of suffering. Or, hypothetically take any tragedy of the commons example, really. Do you really believe that a society where no one votes and everyone defects in the prisoner's dilemma is not suffering in respect to one where people are less reasonable? But I guess the counterargument to this is that a society that's just a colony of economists has never actually existed (thank god!), so we don't know - maybe they wouldn't suffer. Anyhow, this seems to rule out any definition of "reasonable" that means acting rationally, that is, in informed self-interest.
I had a suspicion that maybe "not religious" is meant by "reasonable". Well, that's a bizarre definition, for one thing. But it might possibly be true, except that the less happy atheists of America seem to provide a counterexample. Whether you think American atheists are less happy because they're soulless or because they're victimized by Big Church, you still have to say, some people became less religious, and overall the happiness of people got reduced.
So what does that leave for the quote to claim that is both true and not entirely tautological? The only definition of "reasonable" where this statement seems to make some sense is "not superstitious". So what this quote can be construed to mean, then, is "No group of people ever suffered a genocide, war, or economic collapse because they weren't superstitious enough". I guess it's possible that some time war was avoided because of some "bad omen", which would make it false. But then, maybe not, so then it might be true.
What bothers me is that this is a terribly weak statement, whereas the quote from Harris initially sounds like it makes a quite clear and quite strong claim - we should encourage more reason, since if people are more reasonable, it's always better for society. That's not the claim it makes at all.
