1. Many babies are conceived despite the best laid plans. If she was using contraception properly and fell pregnant, surprise would be an appropriate response.
2. Many people have sex for purposes other than conception. Pregnancy needn't be the expected result of intercourse, and in most instances it isn't. Therefore most people don't live in a constant state of readiness for the condition of pregnancy.
As for soft cheese, it certainly can be compared. Either you think it's ok to dictate what a pregnant woman can and cannot put into her body or you don't.