Arguments for the overturning of the Roe decision can be grouped into two categories: (1) the positivist argument that, contrary to the assertions in the Roe decision, nothing in the Constitution protects the right to privacy in the abortion decision (thus leaving legislatures free to regulate the matter), and (2) the natural law argument that a fetus or unborn child has a fundamental and inalienable right to life (thus preventing legislatures from regulating the matter, except for compelling governmental reasons). The right-to-life movement is grounded upon the latter, natural law position. The difficulty for the pro-life movement is that, if the Court decides to overrule Roe, it will most likely do so using a positivist rather than a natural law rationale.
Raymond B. Marcin, 'Posterity' in the Preamble and a Positivist Pro-Life Position, 38 AM. J. JURIS. 273 (1993).