Child support

I have lost the copy of the Daily Telegraph I saw this in so I am hazy on the details but the gist is there. The story starts with two women who wanted to have a baby so they enlisted the aid of a sperm donor. The donor did not want to be involved with parenting or raising the child in any way, and he wasn't expected or wanted to. However at the time, he was required to sign a document confirming he was the child's biological father. I'm not sure if this was at the behest of the mothers or a local legal requirement. And so everyone should have been happy - a good samaritan does a favour for two people who wish to give birth to, raise and nurture a child as part of their family. But alas the story doesn't end there. A while later, the women decide they no longer wish to be a couple and split up, the child going with one of the mothers (I think it would have been the biological mother but I don't recall if that was mentioned in the article). Not news yet right? But then the biological father is required to pay child support! Now, just call me old-fashioned but that seems unfair. It should be the other mother who is required to be in part financially responsible for their child. Would the donor have been expected to contribute if the child had been the result of an anonymous contribution through a sperm bank or the result of a manufactured sexual liaison to acquire his sperm?