On one hand, the two lesbian “parents” agreed to be responsible for the child and he was doing them a favor, so it is sort of unfair to hold him responsible.
On the other hand, donating sperm to conceive a child to be raised in such a “family” is sick and immoral (though I’m sure in his eyes he was trying to do a “good thing”.)
This child didn't just have a claim on paternal money. He has a right to his whole patrimony: to paternal acceptance, guidance, inclusion in the kinship network on the father's side, which means grandparents, aunts, uncles, cousins, possibly half-siblings; to a normal sense of identity based on the unfolding gifts of body and mind which he got genetically, but which are best understood and best developed by paternal interaction.
That's the big thing.
So, maybe Uncle Sperm was trying to do a "good thing." Is he going to step up and do the right thing? Is Miz Proud Lesbian even going to let him claim visitation?