The Modal Ontological Argument fails in the 2nd statement!
Premise 1. It is possible that an MGB exists.
Premise 2. If it is possible that an MGB exists, then an MGB exists in some possible world.
Wrapped in Premise 1 are the many, many ways people use the phrase “it is possible”.
If someone insists that certain geometrical figure could have an even number of angles, a person could answer this as “possibly” because he or she doesn’t yet know enough about the figure to determine that those geometries ALWAYS have an odd number of angles.
Once enough is learned, what was once considered possible becomes impossible.
And so the Modal Ontological Argument, not being universally true, cannot be a proof.
Wow. Glad to see people love philosophy so much here. I could have predicted this would get almost no responses. 
Scientists are anti-aristotelian.
Do you mean in terms of his four causes?
As for modality, I think it lies at the heart of science: experiments would make no sense without the considerations of counterfactuals (ie what could happened in another possible world with the same laws of nature as ours or with laws that varied in a way the experiment is designed to explore).
Godel had his own version of the ontological argument. Bertrand Russell believed it for a time. It is one of those intellectual puzzles that has fascinated many philosophers.
I think the article does a good job of showing the issues with the version it presents.
I mean in its emphasis on abstract metaphysics. Bacon’s novum organum is aimed squarely at Aristotle and Plato.
That’s dissapointing. Aristotle and Plato are where it’s at.
That being said, the modal ontological argument is not very Platonic or Aristotelian at all. It’s steeped in anglo-American philosophy.
Seidensticker (as usual, from what I’ve read on his blog) comes across as someone who has informed himself just enough to dismiss the argument, and no further.
I’m sure it’s true that some apologists, either unintentionally through lack of understanding, or intentionally through dishonesty, equivocate on the meaning of “possible” in order to make the argument appear stronger. (And yeah, anyone using the ontological argument responsibly should explain the difference between epistemic and alethic modality.) But Seidensticker’s accusation there doesn’t actually do anything against the argument properly understood. Given reasons to think that’s God’s existence is possible (and to the extent that they are better than any reasons to think that his non-existence is possible), the argument still goes through.
In my own blog post on the argument, I give a couple reasons to believe there’s an asymmetry there that allows the argument to succeed.
Moreover, Seidensticker gets sucked into the trap of reifying possible worlds, claiming that premise 1 actually assumes the existence of God “somewhere”, as if possible worlds are actual alternative realities that exist. They are not; “God exists in some possible world” is just a way of saying “it is possible that God exists”. So he is simply wrong to say that the argument is circular.
And then, of course, there’s the usual anti-apologist cans about Yahweh not being all good because of the conquest of Canaan, about the supposed contradictions in the concept of God, and so on and so forth. (I.e. Seidensticker complains about apologists using bad arguments, and then goes on to use bad arguments.)
The biggest hoot was when he completely failed to understand Plantinga making the distinction between the argument being conclusive (which the ontological argument is not) and being rational (it provides some justification for its conclusion, even if not overwhelming).
My own view is that there are better versions of the ontological argument out there: see my blog post following the one I linked here for my favorite. 
Their ideas and the descendants of those ideas are definitely still part of the philosophical conversations.
ETA 2: I would argue that Plato lives on in the views of mathematics and reality that EricMH has expressed, at least as I understand those ideas.
I took @swamidass as referring to Aristotle’s scientific methodology as practiced by him and his followers. The “as practiced” is important, I think, since Aristotle did correct Plato in recognizing empiricism and induction as sources of knowledge of the physical world (and not contemplation of ideal forms and spelunking thought experiments).
But pursuing those ideas is not what Aristotle did. Plus of course Aristotle did not think of Bacon’s contribution of controlled experiments.
ETA: Aristotle’s four causes (especially the “final cause”/teleology bogeyman) are also not part of scientific methodology. And his approach to natural kinds, primary substance, and categories is not scientific methodology. Maybe closer to YEC kinds? I dunno.
Aristotelian hylomorphism makes a come back in Jaworski’s work. His Philosophy of Mind is a very good introduction to analytic Phil of Mind, but with that bias to hylomorphism.
I also need to note this commonality that Jaworski has with Krauss.
Have you seen David Bentley Hart’s critique of the modal ont arg in his The Experience of God? I think he makes a lot of sense. He likes Anselm’s a lot better. For me, this has been the one theistic argument that always sounded like magic to me and probably always will. I think there are many good arguments for God’s existence, and maybe this is one of them, but I’ve never been able to “get” it.
I have not. What is the gist of his objection? I’m surprised he likes Anselm’s argument, because that is one that I think is demonstrably false, as I discuss in my blog post.
Something about it making God a creature within possible worlds. His concern is that, it, like a lot of analytic philosophy, he claims, makes God a person rather than the ground of being. I’m not with Hart or the analytics on this. I follow David Bradshaw on this. But that’s another story.
As for the specifics of what Hart says, I’d have to look.
Ah. He’s a divine simplicity guy. Well, I’m sure he has a response to this, but he’s wrong about that concern - that’s just not what possible worlds mean, and you don’t even need to talk about possible worlds to do the modal ontological argument.
I do wonder if anything Hart’s written can make divine simplicity sound coherent, though, because nothing I’ve seen from Feser has helped me in that regard.
Gödel introduced the modal variant of the ontological argument, and it has been computationally verified as a valid argument.
Gödel’s version has a modal collapse problem, though. Other philosophers, Pruss for example, have developed improved versions of it that use a similar logical structure.
Validity is a nice start. But even the simple argument presented in the OP was admitted as valid at the start of the critique…
Between validity and soundness falls the shadow of empirical reality, to misquote Eliot for posting fun and profit.