They make up lying and mean stories about him because he is not sociable and is only seen at night.
Explanation:
Boo Radley is not a sociable or communicative person. He is a recluse due to his difficult childhood and violent father, the rare times he was seen was the night and yet he does not maintain contact or friendship with any of the citizens of the city. This causes the population to make malicious gossip about him, presenting him as someone who is evil and who kills animals and is dangerous to humans. All of these stories are lies, since Boo is a very kind man who cares about the safety of children, even if no one knows.
"To Kill a Mocking Bird" is a book about racism and intolerance presented by people admired in society who take positions that are considered "just" and "Christian," but that are malicious and dangerous.
