Anselm's ontological argument is, however, bollocks. Merely postulating the existence of a greatest possible being is irrelevant as to whether such a being exists, or whether free will is even possible. There's no evidence that it is apart from our feeling and wishing it were so.
The ontological argument makes a lot more sense when you start from Augustine's viewpoint that evil is always a privation, a lack, and never a thing itself. In fact, it cannot be understood without Augustine's understanding of evil as a framework.