I would keep quiet if I had a famous parent because if not, everyone would act all nice towards me just for some personal favors such as money, autographs, or free merchandise! People who ignored me before would suddenly act all friendly towards me just for their own material wants! I don't like that because I hate it when people act all fake towards others just so they can earn something!
I would not want to be known as having a famous parent as everyone would treat you differently and you would never know who was truly your friend and who was just out for your money or to use you. I do not blame him for not wanting people to know.
When people find out someone is famous, has power or they are related to someone who is famous then they try to get closer to those people. They try to get money, favors, whatever they can out of these people. If my father were a famous author I would not tell anyone and try to live a normal life.
Joe Hill chose his middle name so that he was able to make a reputation on his own. While many people already knew whose son he was, it gave him a chance to develop his own literary style and his own audience. It was the right move for a respected and sustainable career.
I would take great pride if my father was a popular person such as Stephen King. I would not 'come out' just because of the publicity I could receive, but because I think he should be honored for the person he is. Keeping quiet about who I am, I think, would make my father feel upset. I would want the world to know he produced a son that may also become a writer one day.