This is another topic that could go under several categories, but since it concerns the ontological argument I thought I'd put it under philosophy. Now what I'm writing has been brought up by other people in the past, but I thought I'd write about it anyway here and see if there are any objections.
I'm thinking specifically of Plantinga's version of the argument. I've found the argument interesting, but like many I haven't necessarily found it to be something that would convince me personally if I didn't believe and it wouldn't be my first choice as an argument to use for God. Here's Plantinga's version-
1. It is possible that a maximally great being (God) exists.
2. If it is possible that a maximally great being exists, then a maximally great being exists in some possible world.
3. If a maximally great being exists in some possible world, then it exists in every possible world.
4. If a maximally great being exists in every possible world, then it exists in the actual world.
5. Therefore, a maximally great being exists in the actual world.
6. Therefore, a maximally great being exists.
7. Therefore, God exists
According to Craig, P 2-5 are "relatively uncontroversial" among philosophers. I've been studying philosophy in a very amateur way (and frankly I still don't know that I fully "get" the ontological argument) the past few years, but I would think that this would be news to the vast majority of New Atheists who believe that God's existence is merely highly, highly improbable and not impossible. After all, of Dawkins' "seven levels", he put himself at a 6. Anyway, the point is that the "stated" reason that skeptics say they don't believe isn't because its impossible (although the more philosophical ones may go that route more often) but because there's no reason to believe or evidence etc.
Now the multiverse hypothesis is often seen by many of us as a way to escape the fine tuning argument, but my point here is that, with the above in mind, I don't see how the multiverse helps them. Instead, every world that possibly exists does exist if there was an infinite number of universes. To put it in a not-very-scientific way, let's say an atheists grants that there is a 1 in a billion chance that God exists. But there are an infinite number of universes, so God WILL exist in one of them. And by the nature of God, if he exists in one of them then he necessarily exists in all of them. So like the thread title says, multiverse theory could be an actualization of Plantinga's argument. If you said instead a very large number of universes, let's arbitrarily decide on 100 billion, then you could still arrange things in probabilistic terms. Then if you deny the existence of multiple universes (which I would imagine that most would do), then you're back to square one trying to explain away fine tuning.
I'm open to correction if my reasoning is off, in fact that's a large part of the reason why I posted this to see if I'm missing anything obvious. Keep in mind that I don't actually believe in this multiverse and think that it actually should be mocked way more than it is. It almost boggles my mind if an atheist believes there is a multiverse, then he's the one who really believes in unicorns and Santa Clause... at least on a superficial level (most internet skeptics don't go beyond that) it appears to be a laughable and unscientific and very "mock-able" idea (and yet they laugh at us). Just think about that- fuzzy pink unicorns and Santa Clause and tooth fairies and even flying spaghetti monsters, they all fit into the infidel's worldview. Anything as long as its not God.
So any thoughts?