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.
If I was a strident atheist and my life was saved by a Christian fundamentalist, it seems plausible to me that I would subsequently be less prejudiced against such people and less concerned about the areas in which I thought they were incorrect. But not that I would believe whatever they do.
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 remember when I met my first evangelical fundamentalist I couldn't for the life of me figure out why he earnestly believed this nonsense about the world being 7000 years or whatever. It was only when he said that he used to be a homeless drug addict and he was helped out of addiction by a Christian group that it twigged - they showed him kindness that the rest of the world had not.
I'm pretty sure being rescued not only rearranged his whole world view such that the world is 7000 years old. I'm pretty sure it also rearranged his world view to view facts as less important than kindness.