This depends on the particular group of rationalists. An unfortunately outsized and vocal group with strong overlap in the tech community has gone to notions of quasi mathematical reasoning distorting things like EV ("expected value"). Many have stretched "reason" way past the breaking point to articles of faith but with a far more pernicious affect than traditional points of religious dogma that are at least more easily identifiable as "faith" due to their religious trappings.

Edit: See Roko's Basilisk as an example. wherein something like variation on Christian hell is independently reinvented for those not donating enough to bring about the coming superhuman AGI, who will therefore punish you- or the closest simulation it can spin up in VR if you're long gone- for all eternity. The infinite negative EV far outweighing any positive EV of doing more than subsist in poverty. Even managed to work in that it could be a reluctant, but otherwise benevolent super AI such that, while benevolent, it wanted to exist, and to maximize its chances it bound itself to a promise in the future to do these things as an incentive for people to get it to exist.