Christianity Today has an important article that examines why many evangelicals are unmoved by the natural law arguments put forward by prominent Catholic scholars in defense of traditional marriage. Of course, the dualism at the heart of natural law reasoning has come under scrutiny in Catholic circles too: Think DeLubac.
The issues are weighty, but at the end of the day, I find myself closer to the evangelicals than to the contemporary natural law crowd. If our morality is severed from our doctrinal beliefs, we are abetting the secularization of public discourse and indeed bringing that secularization into the bosom of the Church. That is not their intent, but it seems to be an inescapable consequence of natural law reasoning. The evangelicals are right to be suspicious.