Without a moral basis there is absolutely no decent constitutional or legal argument against the practice of abortion. Because, without a moral basis there is no constitution or law. They're just dead letters.
In any case, here is my position on this in detail:
The Equal Protection for Posterity Resolution
A Resolution affirming vital existing constitutional protections for the unalienable right to life of every innocent person, from the first moment of creation until natural death.
WHEREAS, The first stated principle of the United States, in its charter, the Declaration of Independence, is the assertion of the self-evident truth that all men are created equal, and that they are each endowed by their Creator with certain unalienable rights, beginning with the right to life, and that the first purpose of all government is to defend that supreme right; and
WHEREAS, The first stated purposes of We the People of the United States in our Constitution are “to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defense, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity”; and
WHEREAS, The United States Constitution, in the Fourteenth Amendment, imperatively requires that all persons within the jurisdictions of all the States be afforded the equal protection of the laws; and
WHEREAS, The United States Constitution, in the Fifth and the Fourteenth Amendments, explicitly forbids the taking of the life of any innocent person; and
WHEREAS, The practices of abortion and euthanasia violate every clause of the stated purposes of the United States Constitution, and its explicit provisions; and
WHEREAS, Modern science has demonstrated beyond any reasonable doubt that the individual human person’s physical existence begins at the moment of biological inception or creation; and
WHEREAS, All executive, legislative and judicial Officers in America, at every level and in every branch, have sworn before God to support the United States Constitution as required by Article VI of that document, and have therefore, because the Constitution explicitly requires it, sworn to protect the life of every innocent person;
THEREFORE, WE THE PEOPLE OF THE UNITED STATES HEREBY RESOLVE that the God-given, unalienable right to life of every innocent person, from biological inception or creation to natural death, be protected everywhere within every state, territory and jurisdiction of the United States of America; that every officer of the judicial, legislative and executive departments, at every level and in every branch, is required to use all lawful means to protect every innocent life within their jurisdictions; and that we will henceforth deem failure to carry out this supreme sworn duty to be cause for removal from public office via impeachment or recall, or by statutory or electoral means, notwithstanding any law passed by any legislative body within the United States, or the decision of any court, or the decree of any executive officer, at any level of governance, to the contrary.
meaningless