Very few things are about reason. I think to function in the real world you can get very far by just retaining information and being able to follow protocol. You rarely really need to make logical conclusions or know how to test a claim in order to get through life, and having insane ideas is largely inconsequential.
I've always thought religion was the main culprit... I still do, but I do see some very religious people who are able to separate religious and real world thinking... but I still think for less intelligent people religion is often the gateway to "reality is what I want it to be" type of thinking.