Sounds as if your apologetics Prof. needs to do a serious study of the language of Romans 1:17-32. The fact is that most Theologians since Kant have denied (to one extent or another) the existence of natural theology. Barth was most vehement against it. The difficulty with the position is that God's general revelation does not fail to accomplish it's purpose. There is a second difficulty. God in His special revelation, the bible claims that there is a natural theology. There is a clear crisis of authority: If God, Speaking through Paul to the Romans, claims a natural theology, and Kant -> Barth claims that there is not, either Paul (hence, God) or Immanuel Kant must be wrong...there are no other logical alternatives to this statement.
Would you mind giving me a definition of "Natural Theology"? Doesn't Natural Theology say that we can know everything we need to know about God from the things around us using reason?