Jordan Ballor summarizes quite nicely (with all the relevant links) the state of the conversation regarding evangelicals and natural law. Among the links he provides is one to this piece by Vincent Bacote.
Bacote attempts to explain why evangelicals, especially in politics, seem to eschew appeals to what might be called natural law:
Many evangelicals assume mutual understanding when considering how to make a case for the gospel in our current culture. Many of the arguments used to begin a conversation or pursue a persuasive path rely upon the possibility of some agreed-upon claims that at the least make Christianity defensible against skeptical attacks. But this is less the case when it comes to evangelicals and politics. While the tensions in political argumentation often assume strong polarities, they are not all that different from those between say, faith and science. Yet, natural law is not one of the common ways of pursuing common ground in politics. Perhaps this is because of an emphasis on “the Bible alone” or because of an allergy to a tradition often associated with Roman Catholicism. Maybe it is because contemporary evangelical public discourse has often expressed an effort to make moral claims that are both distinctively Christian while also beneficial for all, and the prominence of particularity diverts attention away from natural law discourse.
If I were speaking of the way “unsophisticated” evangelicals engage in politics, then I might be tempted to endorse wholeheartedly Bacote’s suggestion. You use the language with which you’re most comfortable and, above all, you bear witness to your faith.
But there’s also a division among “sophisticated” evangelicals. On the one side, you have those who are “together” with Catholics. On the other, you have those who prate incessantly about “worldviews,” as if accepting postmodern post-rationality. If all the latter mean to do is accept the postmodern critique of the dogmatic rationalism of the Enlightenment, then I have no major complaint. But if they accept the postmodern identification of Enlightenment rationalism with rationalism as such, then I have to run screaming into the first camp and stick with my uncharitable language about their embrace of “worldviews.”