IMO there are two major reasons why in these times rationality is the superior strategy, at least for the type of people drawn to LessWrong and in some parts of the world.
A third reason is that believing in whatever is socially expedient works much better when the socially expedient beliefs have been selected to be generally adaptive. The hunter-gatherer environment didn’t change much and culture had plenty of time to be selected for generally beneficial beliefs, but that’s not the case for today’s beliefs:
The trouble with our world is that it is changing. Henrich focuses on small scale societies. These societies are not static. The changes they undergo are often drastic. But the distance between the life-style of a forager today and that of her ancestors five hundred years ago pales next to the gap that yawns between the average city-slicker and her ancestors five centuries past. Consider the implications of what demographers call the “demographic transition model:”
Each stage in the model presents a different sort of society than that which came before it. Very basic social and economic questions—including subsistence strategy, family type, mechanisms for mate selection, and so forth—change substantially as societies move through one stage to the next. Customs and norms that are adaptive for individuals in stage two societies may not be adaptive for individuals in living in stage four societies.
If the transition between these stages was slow this would not matter much. But it is not. Once stage two begins, each stage is only two or three generations long. Europeans, Japanese, Taiwanese, and South Koreans born today look forward to spending their teenage years in stage five societies. What traditions could their grandparents give them that might prepare them for this new world? By the time any new tradition might arise, the conditions that made it adaptive have already changed.
This may be why the rationalist impulse wrests so strong a hold on the modern mind. The traditions are gone; custom is dying. In the search for happiness, rationalism is the only tool we have left.
A third reason is that believing in whatever is socially expedient works much better when the socially expedient beliefs have been selected to be generally adaptive. The hunter-gatherer environment didn’t change much and culture had plenty of time to be selected for generally beneficial beliefs, but that’s not the case for today’s beliefs: