I would disagree with the author that Catholics have a "clearer" idea of natural moral law simply because the basis for this for ALL Christians is God's law and values HE revealed in sacred Scripture. In my experience, it is Evangelical Protestants (percentage-wise) who more closely follow this intrinsic moral law in practice and that is really where the rubber meets the road, so to speak. If ALL Christians, Roman Catholic or otherwise, would listen to the Holy Spirit and heed God's word for how His children are to live in holiness and love, this world would be a far better place. There's no need to neglect the truth that God STILL allows Christians liberty in areas where He has not stipulated right or wrong, but that ALL things we do must be done through love and to reflect the righteousness of Christ with which He has imputed to us through faith.