I know the Ten Commandments require us to respect our parents. But not all parents are respectable. I am disgusted by the things my father has done. He is old now and needs me, but there is nothing in his life that deserves respect. How can I respect my father without losing my dignity?
Respecting your father doesn't mean that you think he is all good. But surely he can't be all bad. Surely you can think of some redeeming feature, something good your father has done. There must be something for which you can say that he is a worthwhile person. Can't you think of one good thing he has achieved?
I can. You.
Like it or not, you are a product of your parents. No matter how different you are to them, no matter how far you go to avoid repeating their mistakes, you will never be able to change the simple fact that they are your parents. Whether they were good parents or horrible parents, whether they built you up or put you down, they are where you come from.
Your father brought you into the world. If you honestly think your father is all bad, without a good bone in his body, then on some level you will see yourself as another one of his failures. Your existence stems from his. Respect for parents is a base for self-respect.
The fact that he fathered a child who has a clear sense of right and wrong, and is aware of his wrongdoing, means he must not be all bad. He may not get the credit for your moral sensitivity, but he does get some credit for your existence. If nothing else, you can at least respect him for that. Far from compromising your dignity, respecting your father forms the basis for your dignity, because he, along with your mother and G-d, was a partner in your birth.
Respect does not mean accepting his failings or excusing his misdeeds. It means that if your father needs help, you should be there for him. When he speaks, you need not agree, but you must listen respectfully. You have to treat him as a father. Failing that, your self-respect has shaky foundations.
You don't have to respect the life your father has led. But, for your own sake, you do have to respect that he is your father.