I just read a nice blog post at neurowhoa.blogspot.com/2009/03/believer-brains-different-from-non.html, covering research on brain differences of believers vs. non-believers. The take away from the recent study was "religious conviction is associated with reduced neural responsivity to uncertainty and error". I'm hesitant to read too much into this particular study, but if there is something to this then the best way to spread rational thought would be to try to correct for this deficiency. Practicing not to let uncertainty or errors slide by, no matter how small, would result in a positive habit and develop their rationality skills.