I think if you look at the brain as a neural network then it's easy to see how this happens. Not everyone is born to educated parents and receives high quality education. If a lot of the information your brain received growing up was bad, then you can easily reach bad conclusions. The collapse of institutions makes it worse because now no one trusts anything. So to many the information on the internet is as valid as the information in the textbooks. Then if you keep feeding the brain bad information it starts generating bad information. Lately I've been thinking of information as a "substance" that has been diluted by the internet. So the whole "organize and make all information easily accessible" motto of big G and the web in general has had the consequence of diluting the concentration of good information.