Tidus lost his father at a young age (about 7 years old). So he never really had the chance to discuss his feelings in a more mature way. His father for the most part was emotionally abusive and his mother was distant. She passed away shortly after his father, and from Tidus' perspective held a deeper grudge against his father for her death.

Ten years later these feelings have had time to fester, and would not have healed any knowing your father is responsible for the deaths of thousands.

His journey, however, makes him examine his anger and his hatred towards his father. This is important. At the beginning of the game he resents his father in a very childish way. By Bikanel he begins to pity his father. When they finally face Sin, his last out burst of "I hate you," was almost half affectionate.