Amir's attitude towards Issac's comments is that of hostility.
What is the attitude?
When Isaac tries to tell Amir that the problem is not Islam but fascism, Amire replies in a harsh way saying that the British were sanctimonious biullies.
Rather than engaging with Isaac's point about fascism, Amir deflects and criticizes the British. This avoidance of the core issue further indicates an unwillingness to listen or understand. Also, using terms like "sanctimonious" and "bullies" carries a negative connotation and imply that Isaac's position is somehow wrong or inferior.