"In our view, the Court of Appeals misconceived the meaning of the Akron dictum, which was only that a State could not "justify" an abortion regulation otherwise invalid under Roe v. Wade on the ground that it embodied the State's view about when life begins. Certainly the preamble does not, by its terms, regulate abortion or any other aspect of appellees' medical practice. The Court has emphasized that Roe v. Wade "implies no limitation on the authority of a State to make a value judgment favoring childbirth over abortion." Maher v. Roe, 432 U.S. at 432 U. S. 474. The preamble can be read simply to express that sort of value judgment."