If a rational agent seeks to maximize overall personal utility, and if religious devotion demonstrably improves one’s quality of life, then a rational agent will pursue religious devotion, the more sincerely and zealously, the better. For example, I’ve known at least to anti-religious persons who said they will still raise their children based on religious assumptions, in order to secure a moral foundation from youth, and then will deflate the idea of God, hoping that the external moral framework will remain strong, like a papier-mache balloon.
I’m trying to catch the rationalist at his own game. It’s very popular today to calculate things based on rational utility (according to evolutionary psychology and modular cogsci, of course), so there’s no reason, in principle, why a utility-maximizing rationalist would reject religion, unless, garsh, his animus against religion stems from–say it ain’t so!–simply irrational sources.
A true rationalist will most likely be a religious fanatic, even if only on self-consciously utilitarian grounds. It’s weird how a primary argument for sexual license is that people should be given the freedom to follow their inherited impulses, and that repressing our deepest natural inclinations is as dangerous as it is unsustainable. Yet, meanwhile, these same rationalist types will rant all day that the evolved God-instinct, anthropocentric fallacy, etc. should be resisted at every turn, and that giving in to the unsleeping religious instinct is a social evil of the first order.