How do we know what is "greatest"?

Ok, let's enter round 17 (or whatever) on this Onto debate we are embroiled in.

I have a very simple question that I would like any of the supporters of the Onto to answer (Ian I hope you are not alone... other pro-onto's please speak up).

Ian you write "Can you postulate anything greater than an existent omniscient, omnipotent, morally perfect being?" The answer, of course, is supposed to be no, we can not. Another example of where I am go with this is in the excellent quote you gave us from Anselm, "For, it is possible to conceive of a being which cannot be conceived not to exist; and this is greater than one which can be conceived not to exist."

Now here's my straight forward simple question: How do we KNOW that something that exists is "greater" than something that does not exist? Or to say it another way: WHY is "greater" to exist than to not exist?

I recognize that this sounds like a foolish and almost ridiculous question. I'm sure the initial response is, well OF COURSE something that exists is greater than something that does not exist. But seriously: Why? Why is it greater to exist than to not exist.

I anxiously await whatever answer you can provide to this question. I think that this is the major hidden assumption in the onto that does not reveal on the surface what is already taken for granted at the outset. I predict that any answer you give to this question will provide ammo for an assualt on the Onto being either superfluous, dependent upon cosmo/kalam or at least a posteriori thinking, or just plain fallacious. We will see.

What say you?
-Tornado

PS
I think I saw the Zoink careening off of I-25 at a high rate of speed locked in a death spin.

PPS
The newspapers got it right this time: Dewey actually did win. Or, in other words, the Onto's funeral arangements are being made right now by Blunt Mortuary.