As far as cosmological arguments go, I find the arguments from contingency the most compelling. That being said, they’re not air tight and they don’t lead to me conclude that anything like a personal, conscious, intelligent, interactive, etc. God exists.

Let’s look at a few routes of objection:

1) Everything that exists has an explanation of its existence, either in the necessity of its own nature or in an external cause

Here, we can object (as Bertrand Russell does) on the grounds that causal explanations may run out at brute facts. That is, explanatory chains logically could run out at facts which are one way but could conceivably be different. The answer, then, to the question “why this particular reality?” would be “it just is.” Now, is this paradigm intuitively satisfying? Perhaps not. But is it a viable alternative to the paradigm offered by Leibniz? Yes, at least insofar as it should cause us to not confidently view the necessity of a non-contingent causal explanation as undeniable. At the very least, it should cast a shadow of doubt.

As a tangent to that objection, one could take an epistemically-skeptical approach and say that we cannot ever, in principle, know whether the final explanation in a causal chain is necessary or contingent. As far as assessing the Leibnizian cosmological argument goes, this approach would leave us landlocked in agnostic territory.

4) If the universe has an explanation of its existence, that explanation is God

Here, we can object by accepting that a non-contingent cause grounds all of existence but deny that this cause has the properties normally ascribed to ‘God.’ There are two different ways I see of making this objection.

The first route is to accept that the non-contingent explanation/cause is a unitary entity in its own right, separate from the contingent things it creates - but then to point out that this cause may be unconscious, impersonal, and without any trace of intentionality or intelligence. Is this entity still worthy of being called ‘God?’ Well, that would be a matter worth debating. Is it close to the God described in, say, the Bible? Not remotely.

The second route is to flip the paradigm entirely and say that the non-contingent explanation is not a distinct entity which creates contingencies separate from itself, but rather that it is the fundamental substrate of which all contingencies are comprised. In other words, the Substance of reality is necessary but the particular arrangement or information of that substance is contingent. If we want to persist in calling this substrate ‘God,’ then we have pantheism. And on the same grounds as I normally object to pantheism, I would ask why a reality which is structurally identical to a naturalistic reality ought to be called ‘God.’