Paternity - Fathers - and Sperm Donors ?

"Melville, N.Y. - A New York man who said he donated sperm to a female co-worker as a friendly gesture and sent presents and cards to the child over the years likely will owe child support for the college-bound teenager, according to a judge's ruling" - Sophia Chang, Newsday, p.A5, Seattle Times, December 1, 2007.

The article is somewhat confusing, hence some of my thoughts on this matter could be rendered "wrong" if I'm misunderstanding unstated things in the case.

A. "the man's interactions with the child over the years had a patriarchal nature" -per the legal representative of the mother,
B. Per the man - he donated sperm after learning that his co-worker and her (female) partner wanted to have a baby - and her son was born July 26, 1989
C. "The man, married at the time, agreed he would not have any rights or benefits in rearing the child, but the oral agreement never was put in writing..."
D. "But he took the unusual step of allowing his name to appear on the child's birth certificate because he thought it was in the child's "best interests that he would have an identity when he grew older..." (per the man).
E. Before the child's family moved in 1993 to Oregon the man had contact with the child.
F. The man sent the boy money, gifts and cards and letters signed "Dad" or "Daddy".
G. The man spoke to the boy approximately 7 times over the past 15 years.
H. The child has signed an affidavit stating that the man is the only father he's known.
I. Per the mother's attorney: "The fact of the matter is that he held himself out as the child's father for 18 years until he asked for DNA testing."

I have some problems with the conclusion of child support being owed based upon the accuracy (if so) of the statements above.

A. I see nothing of the allegations of the mother - related to the accuracy of the statements of the man and presume that these facts have not been contested. (IF there are discrepancies, one would need to interpret the credence of the conflicting statements).
B. It would appear to me that the man's name on the birth certificate is problematic. IF it could, for example, allow him to carry the boy on his health insurance through work, or otherwise give him rights as the man's child, responsibilities as "the father" would certainly apply. Otherwise there would appear to either be a potential issue of either fraud or the man claiming rights, but not responsibilities.
C. I do not find the issues of the contact that the man had with the boy in itself as establishing "paternity" or being "the father". Assume, for example, that the man had met the mother while she was pregnant and then lived with her for a period of time - where he was "the father" to the child and others. He would be a "step-father", not "father" in legal terms in such a situation most logically. Adoption or other legal actions might establish parental rights and obligations.
D. I find it important to distinguish between the: "deadbeat father" - who is the biological father of a child and would thereby have potential parental responsibilities and in some cases rights and a man or woman who is involved in the life of a child "as a parent". Such a situation might be problematic in the situation described above related to parental rights of the "second mother" in the event of a split between she and the birth mother. I do not see situation of the birth mother's life partner as similar to the situation of this man.
E. It is troubling to me absent other clear extenuating circumstances as to why this man should suddenly be liable for child support, when he had no seeming rights or responsibilities as the child's "father" for the first 18 years of the boy's life. IF he was the "biological father" as opposed to "sperm donor" I could see the right of the mother to demand financial support.

Perhaps I'm missing something here! Thanks!