I don't know what anti-natalism is, but I think you can either create a baby or you can't. Borrowing sperm from someone else and making a baby with it is some ant-like behavior imo. And to give sperm, I think it really matters that it will be used for things outside of your control, and kids made from it will always be lost because they will be conflicted on their identity and who is their father? Their biological father or the person who raised them? And the kid that is made with your sperm is your child technically, and you are just letting many people who you don't know raise your children. Maybe they get raised in an abusive house.

overall, I think it's very very unnatural and doesn't make sense to me.