Some thoughts about necessity
A filler post
Introduction
This week—or, I guess, 5 days ago—I committed to writing a post a day for 7 days. So far, I have largely been able to meet my standards for post quality. Today, I will not be able to do that. But write I shall! Recently I’ve been thinking about the ‘ontological argument from evil’ as presented by Carl Brownson in his dissertation. If you’re inclined to read it I think it’s worth skimming although, to give a harsh but honest review, I don’t think the juice is worth 150 pages of squeeze. But the ontological argument from evil brings up an interesting question: are there good reasons for atheists to think that God is a necessary being? Stating it more precisely, are there good atheistic reasons to think that God is a being such that, if He exists in some possible world, He exists in all possible worlds? Here I sketch one reason to think this is true, even if you are an atheist.
Desiderata
A good reason for an atheist to consider God a necessary being should follow two desiderata: It should be conceptual, but it should not be definitional. If we agree that God is by definition a necessary being, then there is no further motivation necessary. Providing Webster as a reason will cut not ice with the even moderately reflective. On the other hand, we don’t want the motivations to come from particular religious doctrinal commitments. It is not much help to the atheist if she thinks the God of Calvinism is a necessary being, and necessary beings are impossible; at least, it does little in motivating her atheism.
The Sketch
Here is one thought that, unfortunately, will only be amenable to some atheists (and a wider set of theists). Firstly, God is ultimate. This means that God does not depend on anything else for His existence. This strikes me as a plausible conceptual truth about God. Whatever He turns out to be, whichever religion turns out to be right, for a being to be God it cannot depend, for its existence, on something else. Secondly, the PSR is true. Unfortunately I reject this but many people accept the PSR. For those unfamiliar with the rules of inside baseball, the PSR stands for the “Principle of Sufficient Reason” which says that for any contingent thing F there is some further thing F’ such that F’ explains why F is true. There are many famous objections to the PSR (Van Inwagen’s argument that it entails necessitarianism is one reason I tend to be skeptical) but suppose we accept it. There are a litany of contingency arguments that utilize the PSR as a premise in order to demonstrate that a necessary entity exists which explains the existence of all contingent things. I won’t sketch any single specific argument here, but the rough idea will be that you can set up some collection of contingent facts which cannot itself be explained by a further contingent fact and yet, by the PSR, requires an explanation which will thus be necessary.
So how do we conclude that God must be a necessary being if He exists at all from the above? Well, in the first place, if we accept these contingency arguments + the PSR we are committed to the existence of some necessary being.1 Now, God is either necessary or contingent. Suppose He is contingent. Then his existence is explained by the necessary being we are committed to. But then God would not be ultimate, because if He is ultimate, He depends on nothing. So God can’t be contingent. So He’s necessary (if He exists at all).
So the atheist who accepts the existence of a necessary entity which explains all of contingent reality and the claim that God is ultimate must think that God is himself either the necessary entity which does the explaining or does not exist at all. This will, of course, work the same for the theist who holds similar commitments.
Conclusion
We have quickly sketched a motivation for thinking God is a necessary being that should be acceptable both to theists and atheists who accept some contentious content neutral commitments. If a necessary entity exists, and the PSR is true, and God is ultimate (in the sense that He depends on nothing else for his existence) then God must be necessary if He exists at all.
This is contentious. Maybe we are only committed to necessary facts. I’m just providing a tentative idea here though and so I elide these important minutiae.

PSR🤮
At this point wouldn't "God" just be shorthand for "whatever ultimately necessary being is out there"?