It is up to the married individuals what choice they make, not Big Brother gov't dictating what they can and cannot do.
This general principle applies -- or should apply -- to many, many personal choices that adult people make in their lives. We should be consistent in telling "Big Brother gov't" to butt out of our personal lives and affairs.
(Actually, we should tell busybody citizens who push for special interest legislation to control others' lives through force of government to butt out. The gubmint, after all, is us. Those who stand silent in the face of oppression by their buttinsky neighbors are fools.)