In "Fahrenheit 451" Bradbury has suggested the story turns on the input from Clarisse. Why must Clarisse be killed or silenced?
Explore Clarisse's character in detail, explaining her motivations and the values she represents.
You have an interesting question here--why must Clarisse be killed or silenced? Well, look at the impact that one small, short encounter with Montag has on Montag's life. He meets her on the way home from work. Before his meeting with her, he was a content man, happy with life, enjoying everything. But then he meets her, has a 5-minute conversation with her, and bam. He starts questioning everything. Was he really happy? He realizes that he actually isn't happy at all. Her spirit and essence was so different from what he experienced every day that it disturbed him to the extent that he started questioning everything around him. After all of his meetings with her, before she does "disappear," Montag is a changed man. He is unhappy, searching, rebelling, and thinking of uprooting an entire system of society. And, she didn't do this directly--she was just truly happy. She asked questions. Her mere presence forced him to introspect and see himself for who and what he really was. We have all known people that have impacted us in profound ways, and Clarisse was one such person for Montag.
So, imagine if Clarisse wasn't "silenced" or killed. Imagine how many other people she would inadvertantly impact. Montag was ready for rebellion after meeting her, and if she inspired others to do that same thing, their government would have a full-fledged revolution on their hands. And, if other people like Clarisse were allowed in their world, everything would change. So, to keep control of the people, they had to "control" "wild cards" (as Beatty describes her) like Clarisse.
Clarisse's character is the ideal, the type of character that Bradbury is saying has completely died out in their society. She has an active, questioning, thinking mind, and that is good. Montag's society says it is bad. So Bradbury uses Clarisse as a shining flag of an example, that waves in stark contrast to how everyone else is in their society.
I hope that those thoughts help a bit; good luck!