Isn't the fine tuning argument ad hoc?

[Angrboda]

In discussing explanations that involve "goddidit," it's helpful to recognize that explanations have multiple criteria upon which they can be evaluated. Two of the most common dimensions involved are explanatory scope and explanatory power. Explanatory scope is relatively easy to describe and explain. Explanatory scope is the size of the class of things that the explanation covers. Thus, a theory which explained gravity and the behavior of subatomic particles would have greater explanatory scope than one that only explains gravity. The scope of the "goddidit" explanation is effectively unlimited; there is nothing that it cannot explain. The property of explanatory power is a little harder to explain, but basically the explanatory power is a measure of how well the explanation does at explaining the phenomena. When thinking of explanatory power, it's useful to think in terms of how much your understanding is increased as a result of having the explanation. For example, explaining that what makes a car go is that they have an engine inside them doesn't add much to our understanding of how cars go. However, explaining how an internal combustion engine harnesses controlled explosions to channel energy in the form of motion gives you a lot more understanding of how or what is happening. On this score, the "goddidit" explanation fares very poorly, as it basically adds nothing to our understanding of how or why the phenomena occurs. Its explanatory power is essentially zero. In this, it shares its profile with another common explanation, that it was "magic"; magic has unlimited explanatory scope, and basically zero explanatory power. There's another explanation with those properties, "It just happened." All three explanations have essentially the same virtues and vices if you are going by these two measures alone, they are all equally good explanations. Or equally bad. I don't think it a compliment to say that your explanation is offering stiff competition for "It just happened." If that's the best you can say about your explanation, it's time to start shopping for a new one.

(Philosophy of science is not my field. A quick Google search indicates that predictive power, or how well a theory enables us to make predictions is another common criteria, and again, one on which the "goddidit" explanation fares poorly. A brief look at the Stanford Encyclopedia of Philosophy reminds me of complexities I'm glossing over here.)