Liable, not libel. We are discussing responsibility, not defamation.
A woman has a choice to have sex or not in every case except rape, and I fully support harsh punishments for rapists. if she consented to have sex, then she consented to an act that has a decent probability of resulting in pregnancy. The fact that this is even under debate demonstrates how far our society has fallen. Children should, in my opinion, be regarded as a gift, and if the biological parents don't believe that they are, there are thousands of couples who would happily adopt them.