In part one, Montag calls off work, and Captain Beatty visits his home to lecture him on the importance of the institution of the firemen. Montag then questions Captain Beatty about his intuitive, unique teenage neighbor, Clarisse McClellan. Beatty then proceeds to elaborate on her odd, "dangerous" family. The McClellans are a family of non-conformists who enjoy nature, engage in meaningful conversations, and participate in leisure activities. Clarisse is a product of her environment who does not fit in with her peers, is labeled anti-social at school, and is an independent thinker.
In Bradbury's dystopian nation, conformity is championed and independence is considered a threat to the government and society. Clarisse and her family have been on a government watchlist because they are non-conformists, and Beatty firmly believes that Clarisse was destined to be "very unhappy." In Beatty's mind, conformity is peace and happiness, which is why Clarisse is "better off dead."
Essentially, Captain Beatty believes that Clarisse will not flourish in society, have any friends, or be a content consumer because of her odd, independent personality, which would eventually result in her arrest or death.