"Put simply, “seeking venereal pleasure not in accordance with right reason [procreation]” is the essence of “the sin of lust.” Marital sex must be consistent “with the end of the venereal act” or one commits a “vice against nature, which attaches to every venereal act from which generation cannot follow.” If the sin of lust is present in marriage when the sex act is inconsistent with the goal of procreation, only sex performed with openness to the possibility of children is free of sin and divinely ordained."