In Anna Karenina, one of Tolstoy's characters is said to have been acting rightly, but thinking wrongly. The author describes the way in which philosophers invent a structure of words—an "edifice"—to suit their developing theories. These words are common words, but have special meaning in the context of the philosopher's discussion. Tolstoy's character is described as suffering angst over the collapse of such edifices whenever he thinks too hard about them.
By its very nature, philosophy is hard to define. It deals with concepts for which we have a limited vocabulary of concrete words and phrases. For this reason, we must be very careful when choosing words for generalized statements.
When a person makes the statement, "All people love popcorn," he is asserting a broad generalization based upon his limited worldview. If he believes his statement is truth, then he necessarily founds some of his other assertions upon it. For this reason, he may see nothing wrong with serving it as the solitary snack at a party.
He can go on for some time, believing this—unchallenged. However, eventually someone will say, "I don't like plain popcorn." This doesn't shake his belief, but perhaps suggests it be amended to: "All people like some popcorn."
However, the more he mixes with a variety of people and cultures, and the more he reads and watches diverse media, the more likely he is to find someone who says: "I don't like popcorn." This shatters the edifice. What amendment can be made? "Some people like some popcorn"? No kidding. That's a non-statement, and not worth saying.
There are two reactions to this: denial and acceptance. Obviously, this is a silly example. However, to a person who hangs his entire worldview upon a similar general statement, the person who would disprove that statement is a scary person to meet. He changes everything, by collapsing the edifice upon which a life is built.
Consider the implications of the statement: "All people are evil." If all people are evil, then it follows that people are worthless and expendable. Therefore, the leader is he who can acquire the most and control the masses. This is a scarcity view of the world, and inundates everything the person does on the way to success.
On the other hand, if a person acts with good intentions, but thinks all people are evil, he necessarily smothers his own aspirations because he won't do evil, but believes it is the only way to success.
Too many good-hearted people are stopped by wrong thinking.