>I wouldnt hold out much hope of a flat earth tribe being able to deal with objective reality well enough to aid me. I'm pretty sure there is selective pressure towards being rational, it's just really hard to select for and even then probably not the most important thing.

I'm pretty sure there is selective pressure against being rational. Take your drug addict. The flexibility to rearrange his whole worldview likely increased his fitness significantly. Now he has a support network and community, not to mention the help with addition.

To put it differently: While joining rationalist tribe may confer more fitness than joining the irriationalist tribe, the best fitness is having flexibility to adapt to any tribe you can and not be alone.