Er... and that's it.
Of course, it went without question that the only perfect god was the Judeo-Christian one, so the Ontological Argument could only be an argument for the Judeo-Christian god, and no other.
Anselm has been féted through the centuries by Christian apologists for this 'proof' of their god. You still see and hear them trotting out this 'killer proof' at regular intervals and then sitting back in smug contentment as their opponent struggles. What they don't seem to grasp though is that the thing their opponent is struggling with is to understand just how they imagine they've proved anything with it.
And of course, there is always the blissful ignorance, feigned or genuine, that, if it were true, it would apply to any god which would be conditioned on the cultural ideas of perfection being used, one of which might even be non-existence.
So, if you're tempted to believe there might be something in this argument, put it to the test. Go to your window and 'conceive of' (i.e. think about) a perfect car outside.
Did one appear?
Maybe it takes a day or two to work, so if you want to wait a while and check later, please feel free...
Well, okay! Let's put these practical considerations to one side and enter the fantasy world of philosophers and religious apologists for a moment. Let's play with the Ontological Argument to see what we can do with it.
Try conceiving of any perfect thing you like, no matter how ludicrous. Does it exist? According to the Ontological Argument it must do. All you need is to conceive of something and it shall be yours...
I can conceive of a perfect universe. To me, a perfect universe is one where everything about it is amenable to reason; one in which, given the right tools, the right technology and the right understanding, everything can be understood in materialist terms. A perfect universe to me is fully understandable without the need for supernatural explanations. A perfect universe is one in which there is no need for gods or mysteries. A perfect universe is a god-free universe. Exactly like the one we live in, in fact.
According to Anselm of Canterbury, such a universe must exist.
Oops! St Anselm has now proven there is no god.
So, how can Christianity's favourite 'proof' of god prove gods don't exist? How can the same logic lead to two mutually exclusive conclusions?
Because, by simple logic, using a simple mind experiment, we've now proved the Ontological Argument to be the nonsense it always was. The Ontological Argument is like a conjuring trick where even the rabbit is imaginary, or, to put it another way, The Emperor's New Clothes. Who in their right mind was going to put their hand up and say, "Er... rihthámsócn, úre Ár, ðu bist gemaðel sceallan!" ("Er... actually, your Grace, you are talking bollocks!", as a 10th century Englishman would have said it). And who would have listened to them before they went to the stake?
Anselm's Ontological Argument is nothing more than our old friend, anthropocentric arrogance. It's nothing more than the idiotically arrogant argument that a god must exist because I believe it does; that somehow human imagination controls reality in an obedient universe which exists merely to serve the needs of humanity, so 'faith' is enough.
And that of course was exactly the universe which Anselm imagined he lived in and why he and others who shared his arrogant ignorance found his argument so convincing.
I wonder why modern theologians have never managed to update their view of the universe from that of a 10th century cleric who thought the earth was flat, the centre of it all, and all made especially for him.