What do Hiram and Harlan (his father) argue about on a regular basis and why is it an issue?

Upon coming back to Mississippi, he finds that he can no longer be a part of such a prejudiced society and is very vocal about this. The relationship between Harlan and Grampa is very strained because of this and is further complicated when Harlan decides to move to Arizona, taking Hiram with him. Harlan does not want Hiram returning to Greenwood although Grampa invites Hiram to be there every year. This is the cause of many years of arguing between Hiram and Harlan.