I suspect to a large extent the problem is when people are taught what to think rather than how to think.
When people are taught how to think it's easier for them to process the concept of taking the same inputs and drawing a different conclusion, and thereby having at least some respect for people who want to solve the same problem but in a different way. When people are taught what to think there's little to process other than "you don't think the right thing, therefore you are wrong" and from there it's a small step to "you are wrong, you clearly have no interest in being right, therefore you must be a (derogatory term)"
If you can't construct a reasonable explanation for why you believe what you believe then anyone who can present a reasonable explanation that counters your belief becomes impossible to refute. So the person has to either re-examine what they believe (which can be uncomfortable), or write off the other as being "one of those (whatever group)".