Of course, to the philosophers the God everyone believes in is a necessary being. That is, if God exists, he must exist. There's no possible world where God exists but where he didn't need to.
But I don't think this is the end of the discussion because God's necessity is hypothetical. It's a convention of thought used to make it possible to go on with the discussion. So, if we can table the necessity idea I'd like to present a syllogism that is very - if not fatally - flawed, but that can perhaps serve as a thought-starter for more and better ideas.
1. According to traditional Jewish thought, God is utterly unique.*Why is the reasoning suspect? Because to assign a probability to some event or being, there needs to be some real data that establishes base rates. Without actual data and base rates, we're just guessing and assigning the probability in terms of what subjectively seems surprising.
2. Something unique is rare, unusual, and/or distinctive.
3. Something rare, unusual, and/or distinctive is improbable.**
4. God is the single most rare, unusual and distinctive being possible.
5. Therefore, God is more improbable than any other being or occurrence.
The more I look at the syllogism, the less I like it. (1) needs to be unpacked, and (4) gets into the realm of ontological arguments. But I am not really interested in constructing a perfectly solid formal proof so much as trying to support the idea that physical processes leading to the emergence of life on Earth should be no less surprising or believable than the existence of God.
Perhaps another approach is to ask why it should at all be believable that the universe comes from a god or "intelligent designer."
* Comment on (1): This means that there is only one God and that there is nothing like God. Whereas we like to think of individuals as being unique from one another - me, you, Barack Obama, Senator-elect Scott Brown, and so on - these individuals belong to the class "human beings," so other people are like them and belong to their kind. My understanding of the God idea is that nothing is like God and nothing is a kind to which God would belong.
** Comment on (3): I'm not sure that this premise holds up. The lack of real vales hurts because something could be infrequent but at least predictable.