Have you ever actually read the 14th Amendment? It specifically excludes the unborn as citizens or persons to whom the protections of the constitution apply.
"All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws."
The unborn are outside the jurisdiction of the Constitution. They have no more rights under the Constitution than a citizen of a foreign country does. Positive law may include protections for them, but that Constitution is otherwise silent on the matter.
Lets assume for the sake of argument that you are right (legal scholars like Dr. Charles E. Rice have addressed this matter, the meanings of "born," "person", "nonperson", "human" with regard to the 14th amemdment indepth) and that unborn children are left out of the Constitution and the 14th amemdment. The Natural Law given to us by God and make know to us by reason still tells us that the unborn child is a person, a human being, thus with a right to life. Even if the constitution did not cover him (the same way the text was said not to cover slaves) murder could still never be endoresed or allowed under cover of law.