I want to run something by you to get your opinion. The KCA and fine-tuning arguments are presented as philosophical/logical arguments with some scientific premises. Some skeptics that don’t like philosophy will dismiss it and appeal to scientism.
But if we look at something like the detection and declaration of black holes, aren’t they doing the same things? They aren’t looking at direct observation but instead looking at effects and making inferences to the best explanation for the cause. If that is accepted as science then the KCA and the fine-tuning arguments should be as well.
I’m not interested in declaring the KCA and fine-tuning to be science but I’m thinking that an analogy such as this might be useful when a skeptic cries god-of-the-gap.
This is a very interesting question. The philosophical and scientific nature of the arguments I’d make a distinction in is that the arguments themselves are philosophical and are supported by science. The fine-tuning argument is particularly interesting because it’s rooted in the nature of efficient causation and information theory–philosophy of science. I’ll need to unpack quite a bit concerning methodology and the realist/anti-realist debate.
You’re correct in that when we detect black holes we aren’t detecting the objects themselves but the effects it produces and making an inference to the best explanation for what the cause could be. When considering the use of abductive reasoning in science there is an assumption, or suppressed premise, of scientific realism or critical realism. (I am a critical realist, which is to say that scientific models actually describe the world and must approximate truth. I don’t have to make the commitment that the models are the whole truth.) The limits of observation are a subject for empirical science, and not for philosophical analysis. Thus, a theory is empirically adequate if and only if what it says about the observable things and events in this world is true. The conclusion itself may be contested but this methodology may certainly be compatible with a realist empirical methodology (a la Darwin). I think pressing the point of Darwin’s methodology would hit closer to home for the proponent of scientism because Darwin used inference to the best explanation.
The French philosopher Pierre Duhem (1861-1916) was a prominent contributor to the realist and anti-realist debate who served as a catalyst for the future development of constructive empiricism (CE), form of anti-realism or critical non-realism. Duhem argued that scientific theories cannot be taken as literal descriptions of reality because theoretical descriptions are idealized in a way that the world is not.
Empiricism set limits on what one is rationally obligated to believe. There is no commitment, under CE, to believe the truth of the theory but one can accept the empirical data. This is very modest in its commitment to the informative power of a theory. If one chooses an informative theory over a less committal counterpart then it can only be for pragmatic reasons and not because these theories are more likely to be true. According to CE, scientists need never accept the need to postpone theories [due to the need of more evidence] or use inferential methods such as abduction as forcing them to go beyond the limits of observation. The explanation of the data can never have a legitimate inference to the best explanation outside of the evidence.
Duhem also stripped any explanation metaphysical import from explanatory hypotheses. This meant the removal of agent causation from acceptable scientific data and since his methodology does not allow for the explanation to go beyond the data, contra abduction, agency was not permitted as a viable scientific explanation. If the aim of a physical theory is to explain phenomena in terms of the ultimate nature of their causes then physical science becomes subordinate to metaphysics and is no longer an autonomous science. Due to the very nature of this approach it entailed methodological naturalism, which is only allowing physical entities to be considered scientific.
The reason why Duhem’s methodology should be rejected is because of the robust explanatory power of realism and abduction as well as the legitimacy of agency in a scientific hypothesis. This scientific methodology is known as Augustinian science, after St. Augustine. The Augustinian approach to science eschews methodological naturalism and employs religious or metaphysical commitments. One need not import any religious commitments to the fine-tuning argument. However, the argument does require the metaphysical commitment to agency. Also, note that the argument still works given a CE approach. A stronger case for fine-tuning can be made using Augustinian science but the fine-tuning argument can stand on common ground of Duhem if need be, given CE and the treatment of theoretical entities (mind) as pragmatic tools. Agency, or mind, is important since it will serve as the explanation for the origin of information for the fine-tuning argument and agent causation for Kalam (an agent is the only known entity that can initiate and cease a series of a causal chain of effects.)
Without getting into both arguments and sticking to methodology and rationale, I think the point you bring up about IBE is best purported when the Kalam and the fine-tuning arguments are presented abductively. I haven’t really seen Kalam set up in an abductive argument, but then again I haven’t given much focus in constructing one or searching for one. Concerning the fine-tuning argument I think it should be set up abductively as well. You can see my use of the fine-tuning argument here: “The Fine-Tuning Argument.” (Also, “Why Inductive Fine-Tuning Arguments are Weak” and “Why Deductive Fine-Tuning Arguments are Weak.”)
Those who do not take the philosophy of science and methodology seriously, or simply don’t know anything about the philosophy of science, are the only ones who make the ‘god-of-the-gaps’ objection. A robust philosophy of science and epistemology is essential in constructing these arguments and pointing out the error in making such a silly objection.
 Bas van Fraassen, The Scientific Image (Oxford: Oxford University Press, 1980), 56. (Who is no friend to abduction.)
 A.F. Chalmers, What Is This Thing Called Science? ed. 3 (Indianapolis, IN: Hackett, 1999), 241-42.
 J.P. Moreland, “The Physical Sciences, Neuroscience, and Dualism,” in The Nature of Nature, 843.