You clearly have no concept of
Contract Law.
Contract law defined and explained with examples. The branch of civil law that deals with interpretation and enforcement of contracts between parties.
legaldictionary.net
Two parties were involved, the man and the woman. Each consented to a contract with known, potential outcomes. What you are trying to claim is that if the woman gets pregnant (a known potential outcome), she has no duty or responsibility to tell the man involved and gets to make all decisions regarding that pregnancy herself. The man could remain completely unaware she is now pregnant.
If she decides to have the child and does, suddenly she has the right to spring on the man--his having had no say to that point--that the child is his and demand he pay 50% of the cost of raising it.
That's not how contracts work. In a fair and normal contract, she has a duty and responsibility to inform the man she is pregnant, and he has 50% of the responsibility for decisions about how things will proceed. If they decide on an abortion, he pays 50% of the costs of that. If they have the child he is 50% responsible for the costs of raising it. That's fair and equal.
What you want is nothing more than the argument of a petulant child. You want it both ways in favor of the woman. That's neither fair or equal, and it sure as hell isn't contract law.