Erroneously covered before and again now imho.
To be a citizen under U.S. law and the Constitution one must be born or naturalized.
If you know of a legal argument whereby the unborn are citizens then say so.
Otherwise any argument based upon the citizenship of the unborn is erroneous.
They are persons - in my view of the law - and not to be deprived of life without due process of law. And, as you point out, the Constitution was established to ensure liberty to ourselves and our posterity - but that doesn't establish citizenship of the unborn. That is a different argument - a facile one.