There were two points that you are not aware of. First, mixed marriage’s between blacks and whites was considered immoral because blacks were not accepted as human and lacked a soul. Read Scott v Sanford Decision of 1857. This decision declared that since blacks are not ‘persons,’ they have no constitutional rights. You cannot compare this with same sex marriage because TRUE love is in giving and sharing yourself by bringing another person into the world, (if possible) through pro-creation.