I'm tempted to brush this off as too simplistic. It levels the field too much. But, at the same time, he has a valid point. Perhaps my reticence is that far too often I've heard this argument used as an excuse for indifference to injustice.
But, if one is really committed to doing the will of God, how can it fail to overflow into social action? Unless one does a major editing job on the biblical text, there is no way one can escape the social ramifications of being a Christian.