I read this book recently for class.
I'd say it is Amir considering his attitude towards his friend (half - brother) Hassan as a younger child. Amir betrayed Hassan by not telling anyone when Hassan got r*ped. After the incident, he began to avoid and act cold towards Hassan, slowly breaking their relationship and distancing them apart.
Furthermore, Amir lied to his Father that Hassan stole his birthday gift, a watch, in order to drive Hassan and his father out the house. He couldn't stand knowing he had done nothing about the r*pe and didn't want to reminded of his lack of help.
Amir, as a Pathan, is able to discriminate against a Hazara (Hassan) because of the social - political context of Afghanistan.
Hope this helps !
