Even then that might not always be the case. Sometimes there are severe time or bandwidth or energy or other constraints that preclude carefully collecting data and thinking things through. In those cases a heuristic that is very obviously not derived from any sort of critical thought process might well be the winning strategy.
There will also be cases where the answer provided by the rational approach will be to conform to some other framework. For example where cult type ingroup dynamics are involved across a large portion of the population.
Exactly right. It is not rationalism per se that is the problem, it is the way that The Rationalists are implementing it, the things they are choosing to focus their attention on. They are worried about things like hostile AI and Roko's Basilisk when what they should be worried about is MAGA, because that is not being driven by rationalism, it is being driven by Christian nationalism. MAGA is busily (and openly!) undermining every last hint of rationalism in the U.S. government, but the Rationalist community seems oddly unconcerned with this. Many self-styled Rationalists are even Trump supporters.
I'm sympathetic to the idea that we know nothing because of the reproductive impulse to avoid doing or thinking about things that led our ancestors to avoid procreation, but such a conclusion can't be total because otherwise it is self defeating because is is contingent on rationalist assumptions about the mind's capacity to model knowledge.