I don't know if it's active "betrayal" so much as the self-centered or naive notion that they will never have to face such a difficult choice, so therefore no one else needs it either. Daughter raped? Couldn't happen. Second-trimester going so wrong that unless the fetus is extracted it could kill the mother? Myth -- (right?)
Not being a woman, I don't know for sure, but it's hard to believe that this degree of cruelty is so common.