Violence is definitely not the core of this novel, and in fact only plays a small part.  The central theme in the Kite Runner is redemption; the bulk of the novel focuses on Amir's intense desire for his father's approval and his guilt for not protecting Hassan.  From the time he leaves Afghanistan until the time he returns with Sohrab, he is struggling to redeem his past sins and find a way "to be good again."  This clue is given on the very first page of the novel when Rahim Khan calls from Pakistan.

Violence is not the core of the novelThe Kite Runner; the story line and characters definitely offer a critique of violence, but ultimately this book is about the enduring power of love and friendship to overcome the harsh violence in the characters' lives.