The human brain has a tendency to discount new ideas that conflict with existing opinions.
This is why Republicans tend to watch Fox and Democrats tend to watch CNN. Each network propaganda machine skews news in a way that conforms to right/left per-conceived ideas of what is "true."
When someone is given information that directly conflicts with what that person believes to be true, the person can either examine it (if they are intellectually curious and honest) or dismiss it out of hand (if they are intellectually incurious or dishonest).
Some people will be so offended by the new information that they will become angry and will lash out.
Of course, there are the trolls, too, who are just out and out dishonest.
I remember the first time I heard someone claim that 9/11 was an inside job. It was actually a guy from Germany, of all things, and he showed me how to fold the US$20 bill so that you can see the twin towers on fire. I had to admit it was interesting, but I essentially dismissed his claims. Dismissed, yes, but his words had an impact on me. A couple of years later while surfing the 'net, I found someone else make a similar claim. That's when I started looking into it for real, and one I ACTUALLY EXAMINED EVIDENCE FROM BOTH SIDES, I concluded that the official story is a lie.
So, the key is that a person has to be willing to examine evidence from BOTH sides of an argument, just like if they were on a jury.
Most people take the shortcut and just dismiss. But the real question is whether or not that person is really intellectually curious and honest. If they are, they might eventually come around. If they are not, then they are not worth wasting time with because they are anti-intellectual and that is a person you do not want to associate with.
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