Religion reduces people's ability to use a good brain and leads to them rejecting truth whenever it conflicts with belief. It's unfortunate that the brain has such poor anti-virus evolved into it, because once a mind virus is installed and takes on the role of anti-virus, that brain is usually shackled for the rest of time while its owner is rendered a zombie.

It's crucial to install proper anti-virus early on, and that means training young children to reason properly and to stop believing everything they're told by authorities - just feeding them truth isn't enough because that doesn't teach them to think for themselves, so a better way to bring up children may be the way my father did it with me. He provided me with all sorts of fake knowledge which he knew I would be able to disprove and reject: he systematically trained me to question everything and never take anything on trust. If any of that fake knowledge wasn't sufficiently obviously false, he would build upon it until belief in it became unsustainable. Becoming good at working out whether I was being fed truth or lies was essential to avoid being laughed at. Oddly enough though, he did this as someone who was very religious having been brought up to be a Christadelphian, and it never occurred to him that I would reject his religion too as a result of this training, but the eventual result was that I converted him to atheism (after a couple of decades of heated arguments - it takes a long time to deprogram people even if they're rational).

The greatest example of all and sadly overall humanity not always learn from previous mistakes: The dark ages