This is largely because of the highly emotive nature of the sexual abuse of children, resulting from the perceived innocence of youth, the vulnerability of children and social conceptions of these child abusers as evil and beyond help. (politics.co.uk)
A married couple can morally choose to make use of the infertile period to avoid the conception of a child where proper reasons exist, and Humanae Vitae does spell out the nature of such reasons. (faith.org.uk)
It is a condition of sexual activity being marital that it should be a generative or procreative type of act [1]-- the type of act which, if the couple are fertile, can lead to the conception of a child. (faith.org.uk)