"[U]nder Roe, even a viable fetus is not entitled to constitutional protection in its own right: it must depend on what the state may consider a compelling interest. If the state decides not to protect the “potentiality of life,,”a viable fetus would not enjoy any protection in the abortion context. The only conflicting interests, as seen by the majority, are those of the woman and of the State. The rights of the fetus (and, possibly, of the father) have been completely ignored."