Indeed, I do believe that modern moral and social values stand quite well on their own outside of the writings in any particular ancient book; this is the only way to pose an argument that the militant secularists cannot simply pass off as "religious fundamentalism".
Alas, even this method of showing a "secular viewpoint"--whether or not it's an affected one--won't convince the hardened leftist moral relativist--or five supreme court justices. They can just say that the author is repeating a thinly-disguised sectarian "natural law" argument. "Is it any coincidence" they'd say, "that a Polish student makes an argument straight out of the Catholic natural law tradition?" Argument dismissed.