who have some obvious rational thinking skills and yet are so incredibly stupid and gullible

They're lying. Seth is lying. At best, people like that sometimes they outsource their critical thinking and analysis of politics to the media and "trusted sources". This is still completely intentional - like a crime boss not asking his subordinate how he does his dirty work, for plausible deniability. That way if you back them in to a corner and actually prove them wrong on something they can always say "Well *I* didn't know that. I have to work with the information that was reported. It was fact-checked as true at the time. The science has evolved." So-called journalists and academics all work the same way, sourcing other journalists and academics until you get to the original source who outright fabricated her report.

In this case the trusted source is simply a circle-jerk of friends all nodding and agreeing on the same thing.