My initial research indicates that this is probably the case, if you substitute "researchers in particular disciplines" for "we." Apparently, this began in earnest shortly after WWII, when economists, strategists, AI researchers, and geneticists all adopted a re-interpretation of Enlightenment-era views of how people behaved in society, based on a highly-selective and out-of-context reading of their work, in order to make their own work more easily quantifiable. Being experts, their work informed public policy in the late 20th century, and so their ideas filtered out into society at large. I've posted a couple of documentary essays I've found while researching this, if you're interested. One is on game theory, and another is on the computer metaphor.I think that the reason that we want to believe in a rational mind, is because it provides a framework within which we can predict other people's reactions and responses, and therefore allows us a consensus in which we can operate as a society.