The Ontological Argument - valid or debunked?

[SteveII]

As Irrational said, it is important to understand the S5 modal logic that if something is even possibly necessary, it is actually necessary. (which would answer Kevin's question about the jump from 2 to 3.)

Then I would point out that "necessity," where it isn't supported in any way, is not different than a petulant foot stomp and a yelled "because I said so!"

I need to clarify. The difference is between epistemic possibility and metaphysical possibility. Epistemic possibility is simply "for all we know something is possible". On the other hand, to illustrate metaphysical possibility take a math equation 24673244/8=3005567. While we might say "for all we know" this might be true, but if it is true, than it is necessarily true if it is false than it is necessarily false. If a maximally great being exists, it exists necessarily in a metaphysical sense. Therefore, God’s existence is either possible or impossible.

@Esquilax, one of your objections to maximally great being is that something "slightly more great" can be imagined makes no sense. What could be greater than an omnipotent, omniscient, morally perfect, and necessary being?

An omnipotent, omniscient, morally perfect, necessary being that can eat the one you're proposing. What's greater than that? Same deal, but it can eat the one preceding it. And so on. And so forth. Greatness has no upper bound.

Then you have simply changed the definition of omnipotent. Equivocating. An omnipotent God could prevent getting eaten. 

More importantly, did you just not notice that this argument of yours is just one big argument from incredulity and ignorance? Your inability to fathom something greater is not an argument against my position.

First, at most that would undercut theistic belief, not that theism is false. Second, a limited grasp of God's properties does not entail that our conception of God is false. Third, we can believe in God without being able to grasp all there is to know about God (because that would be impossible).