Catholic understanding of conscience:
Deep within his conscience man discovers a law which he has not laid upon himself but which he must obey. Its voice, ever calling him to love and to do what is good and to avoid evil, sounds in his heart at the right moment. . . . For man has in his heart a law inscribed by God. . . . His conscience is man's most secret core and his sanctuary. There he is alone with God whose voice echoes in his depths (Catechism of the Catholic 1776 quoting Gaudium et Spes 16).In other words, the Catholic understanding of conscience is that every person's conscience is rooted in a objective truth that leads to God. America's understating of conscience is based upon the latest fad and whim.
So until America regains the lost guiding principle of a person's conscience being rooted in truth and foregoes the poison of moral relativism, a conscience clause will not happen.