I'm not currently a SP but my SS's BM is. If you were receiving child support and shared custody of your child, would you insist, well demand, that BF also help with diapers and clothes?
ETA: I have a LO, but his father is not in the picture at all of his own choice. When he was, I didn't ask for child support or help. LO is my child, and therefore my responsibility to raise. I didn't see the point in forcing someone to pay child support and for the next 18 years have a connection to myself and my LO if they didn't want to. So, it's not like I don't understand raising a child, I do.