I mean take right-wing arguments (given that HN and a lot of the internet is mostly left leaning), to them, blaming immigrants for a lack of jobs and keeping them out to preserve jobs is completely rational. Cause and effect, obvious solution, etc. Anti-vaxxers and other pseudoscience movements that have sprung up recently also feel perfectly rational about the BS they're sprouting. I mean from what I can see from here the earth is flat, that's a rational observation to make.