The funny story about the Ontological Argument is that when formulated, one feels that something’s just not right about it, and yet one finds it difficult to articulate what is not right about it. My sense is that it begs the question because it assumes that there must be a God. But this is my general feeling about it.
A more interesting observation about the ontological argument is that a more perfect God than the God of Anselm is a God who is able to “not exist”, as well, neither in the mind alone nor in actuality.
Now, it seems to me that the God of Christianity is one that is always present (i.e. one that cannot “not exist”). However, I can see Anselm, and perhaps some modern theologians, too, entertain the idea that God can indeed cause himself to cease to exist. After all, if they say that God cannot cause himself to cease to exist, then I can reject the ontological argument by showing that there is a more perfect God than the God Anselm believes being perfect, and that is a God who not only must exist in the mind alone and in actuality, but also is able to cease to exist.
On the other hand, if they accept that God can cease to exist, perhaps it is also possible that God can ceased to exist for ever after the creation of the universe; for example, God was the Big Bang, and right after the bang he ceased to exist, which would explain why the world is riddled with evil. Furthermore, the possibility that God can cease to exist, leads me to the idea that God needs humans in order for him to make sense; without humans, the existence of God with his attributes and miracles would be utterly meaningless. Conversely, if God can cease to exist and indeed he has done so, it makes no difference for humans because the world with its laws functions anyway, and life nevertheless has a certain meaning.