I was reading a little of John Piper's story today. Interestingly, he started quite vigorously opposed to determinism, which he now interprets as being opposed to the sovereignty of God. He was a strong proponent of free will when he went to Fuller.
What often happens psychologically when someone is so zealous for one position is that s/he becomes over-aware of the weak points of his/her position. These have a way of eventually overcoming you to where those weak points become the centerpiece of a diametrically opposite you. So in Piper's case, the rather unusual and atypical verses in Romans 9 came to dominate his understanding.
So beware of zeal--some of the most ardent fundamentalist zealots end up being some of the most militant atheists. Moderation in all things is almost always the best policy.