Read this excerpt from an article titled "dangerous ideas": in most cases, books are challenged or banned because they introduce ideas or topics some people would prefer not to examine, or address issues that some find difficult to think and talk about. for example, many people object to books they consider to be obscene because they oppose the use of swear words and vulgar language in the book, or because ideas expressed in the book about race, gender, social class, religion, or drugs don't align with their values. what is the author's purpose in this excerpt?