Sex requires two people. How is that zero contribution? And furthermore, abstinence is a two way street as well. Seems fair to me. Both partners fertile. Both don't want baby. Both don't have sex.

Same ethics with a condom. Both fertile, both don't want baby, both have a dimished sex act with a barrier between them. I've never used a condom so I am assuming about equal diminishment of the act for the man and woman.

What you propose is women shoulder all the risk of harm for the same benefits while the man assumes no risk.