The morality of human extinction

Suppose that a social practice emerged that led people to disvalue parenting and thus to forebear from having children.  Also, this social practice enabled all individuals to lead peaceful, prosperous, and valuable lives.  Suppose also that at some point all of humanity comes to engage in this practice, thus leading all of humanity to disvalue parenting and cease having children.  As a result, this practice leads to a point where humanity eventually dies out: the human species goes extinct, but in the process all individuals lead valuable lives, maximizing goal and desire satisfaction.

The question is this: if a social practice were to lead to all people living valuable lives but also to the extinction of humanity, what is the moral status of such a practice?  Is extinction a moral bad?  Why (or why not)?  Particularly on a contractarian account of social morality, why should I care about human extinction?  What does/doesn't this say about the normative significance of evolutionary stories (such as found in chapter 3 of Gaus, The Order of Public Reason)?