He just didnt know how to express himself, he was so into blitzball that I guess he never interacted so closley to a child before. So, when he had a child he just didnt know how to treat him. But Jecht did want Tidus to become a strong able child, and thats why he didnt want Tidus to cry.. because he wanted tidus to face his problems and solve them without pain. He loved him, hes just one of those macho men that cant admit that they are REALLY sensitive :p
In truth i believe that Tidus’ mother was the bad parent.