Apparently systematic, logical thought makes too great a demand on people.
From what I have seen, most people leave study behind when they leave school–except for what might be required to keep a job. They prefer passive entertainment.
That’s one clue. Another clue is this: people do not like to think of themselves as ignorant (or stupid), and so will fill in the gaps with something, and that something must be easy to understand or to accept without understanding. Remaining gaps in knowledge often are deemed “unimportant”.
Another fact is that people prefer comfort to truth, and one’s comfortable thoughts and beliefs tend to be those that one already has (perhaps even from childhood), or those that flatter oneself; these thoughts and beliefs are then simply assumed to be true.
And some people gravitate to what they consider “special knowledge”, such as various conspiracy theories, or “alternative” beliefs.
Research also shows that people tend to believe what their in-group believes, even against evidence to the contrary.
We cannot ignore the fact that there are actually delusional people, genuinely stupid people, and dishonest people. Apparently there are also genetic tendencies toward being conservative versus liberal and toward various other character traits.
Nor can we ignore the nonsense promulgated by the mass media.
In sum, I believe people generally don’t want to think hard about much of anything, believe they know enough, and believe they know the truth.
So, if someone agrees with you about something, you have to wonder how he or she arrived at that conclusion. And how did you get there?!