I'm having a bit of a problem with my sons biological father. He has not been there for my son since birth. But, my son has his last name. This other guy has been taking care of my son since he was 3 weeks old. My son is now 8. And he wants to have the guy that has been taking care him last name. I called the sperm donor (just being nice) and I told him. His answer was "if I change his last name he hope I die!" but let me remind you that I can count on 1 hand how many times he has seen my son and on that same hand how many times he got any thing my son needed. He also told me that "I don't want my sons name changed because he might grow up to be something in life." I just want to know am I wrong for Wanting to grant my son's wishes.

Not at all wrong. Its important for a child to feel tied to his parents (present parents - not absent ones)