Frankly, what makes his son look bad is his own inability (or disinclination) to stand up on his hind legs and object to the old man's noxious garbage.
Any time we attempt to judge another person's motives, we are walking on very thin ice.
Having said that, here's a potential alternative motive to Mel's refusal to publically 'object' in a strong fashion to his father's comments.
Perhaps Mel views God's commandment to honor your parents as more important than meeting the public's expectations about what he should or should not do.