Oppy's main contention is that a successful argument is one which OUGHT to persuade all reasonable people about the conclusion, not one that ACTUALLY persuades such a people. So, his criterion has a normative character, not a purely descriptive one. Therefore, even if an argument actually doesn't persuade a reasonable person, it still could be a succesful argument provided it OUGHT to persuade such person.
With this in mind, let's consider the Kalam Cosmological Argument for God's existence:
1-Whatever begins to exist has a cause
2-The universe began to exist
3-Therefore, the universe has a cause
The first premise, which is known as "the principle of causality" seems to be more plausible than its denial:
-It is essential to science, since science's main purpose is to explain phenomena in terms of causal laws and mechanisms (e.g. you explain the coming into being of new biological species in terms of natural selection plus random mutations; scientific materialists explain the coming into being of consciousness in terms of brain processes; physicians explain the coming into being of a new diseases in terms of a new virus or toxic substance; and "skeptics" like James Randi explain a fake psychic's feats in terms of magician's tricks).
-It is essential to human activities in general. If under your bed you discover 1 million dollars, you would seek the cause for such money appearing there. It would be pretty irrational and silly to think that such money appeared there from "nothing". It is more plausible to think that it has a cause (e.g. someone stealing the money and putting it under your bed).
No detective, police or judge (in a courtroom) would accept, as a reasonable argument, the atheist's claim "The causal principle is not universal nor obviously true. So it is possible that such money appear under my bed uncaused from absolutely nothing at all, like the whole universe"
-No counterexample exists to refute such a principle. There is not scientific, nor non-scientific, evidence for the denial of the causal principle, namely, for the claim that "something come into being uncaused from nothing". Common examples mentioned by atheists, like virtual particles coming into being from the quantum vacuum, are simply egregious abuses of science, since the quantum vacumm is NOT nothing, but a physical structure which contains energy.
The second premise of the Kalam Argument is widely accepted by mainstream cosmology. And according to world's leading cosmologist Alan Guth, only"crackpots" deny the evidence for the universe's beginning:
Given the truth of the first and the second premises, the conclusion follows deductively: the universe has a cause. Why should be the universe, which began to exists, to be the exception to the causal premise?
It is pretty obvious that the only motivation to deny the causal premise is the theistic conclusion implied by the universe's beginning.
Now, is the Kalam Argument a successful argument in the light of Oppy's criterion? I think it is.
Given a basic knowledge of how science works, common sense, personal experience and rational reflection, the two premises of the Kalam Argument are more reasonable than their negations, and hence OUGHT to be accepted by rational persons. It follows that people who denies such argument are irrational, since they are denying premises that they OUGHT to accept (and that in fact they accept in any other context outside discussions about God's existence).
However, Oppy himself (who is not a theist), doesn't accept the Kalam Argument (and he's one of its main critics). For example, regarding the premise "Whatever begins to exist has a cause", Oppy complains: "before we can assent to the claim that there is an efficient cause for the coming into existence of any thing, we need to be told a lot more about the analysis of efficient causation" (p.152)
I don't think that we need to be told more about the analysis of efficient causation in order to accept that the causal principle is true (and more plausibly true than its denial or negation). Even if we don't have an exhaustive analysis of efficient causation, the latter notion is sufficiently well understood as to be used by science, common sense and normal human activities, and atheists and "skeptics" appeal themselves (implicitly or explicitly) to such principle when the propose alternative scientific explanations for paranormal phenomena, UFOs sightings, putative healings by alternative medicines and so forth.
You don't need to be told "a lot more" about efficient causation in order to know that bacteria often causes diseases; that antibiotics often cause the death of bacteria; that (if Darwinism is right) natural selection plus random mutations cause evolutionary changes and the coming into being of new biological species; that some mutations cause the coming into being of tumours and cancers; that (if materialism plus neuroscience is right) the brain causes the coming into being of consciousness; that the placebo effect is the efficient cause of the apparent efficacy of homeopathy and so forth. (Note that "skeptics" and atheists agressively defend all of these modes of efficient causation to explain a bunch of phenomena, including NDEs, and no cavils or complains about the "need to be told a lot more" on efficient causation is mentioned in these cases).
Again: efficient causation seems to be largely unproblematic or reasonably well understood and accepted by atheists themselves when they accept, believe and defend, sometimes agressively and invoking "science" is their main argument, that the brain produces consciousness (and that NDEs are a brain phenomenon), or that the placebo effect is the efficient cause of the apparent "healings" of homeopathy, that Uri Geller's spoon-bending are caused by magician's tricks and clever deceptions, or that a given UFO sighting was caused by the Venus planet plus enviromental factors.
But when we need to explain the universe's absolute beginning, then SUDDENLY atheists become skeptical of the causal principle and complain that we need much more to be told about the analysis of efficient causation in order to accept that the causal principle is true. The science which they defend agressively in any other context in order to support atheism (and which is based on the consistent application of the causal principle to whatever begins to exist and which allows scientists to seek and find the causal factors and laws responsible of the coming into being of natural entities and events) becomes a matter of doubt and contention when the issue is the universe's beginning.
Many atheists laugh and dismiss condescendingly as scientifically ignorant and virtually impossible any suggestion that paranormal efficient causes could exist and be operative in the world (e.g. faith healing or psychokinesis), but when it comes to the universe's origin, they're prepared and free to say, like atheist philosopher Quentin Smith, that "The fact of the matter is that the most reasonable belief is that we came from nothing, by nothing and for nothing... We should instead acknowledge our foundation in nothingness and feel awe at the marvellous fact that we have a chance to participate briefly in this incredible sunburst that interrupts without reason the reign of non-being ." (Theism, Atheism and the Big Bang Comsology. P.135. emphasis in blue added)
This is a clear example of special pleading, double standard regarding the universe's coming into being and wishful thinking, suggestive of self-deception and (in some cases) of intellectual dishonesty.
Why the universe, which began to exist, has to be an exception to the causal principle that "Whatever begins to exist has a cause"? Why exactly? What (non-question begging in favor of atheism) reason exist to think the universe's beginning is the exception?
Is more reasonable to think that something (e.g. universe) come into being "from nothing", "by "nothing" and "for nothing" than to think that the univere came into being by a trascendent, non-physical, non-material and superpowerful, intelligent and personal cause? Is "nothingness" a satisfactory scientific or non-scientific explanation for the universe's beginning to exist/coming into being?
Note carefully this: Atheists who accept such position reveal that for them ANY explanation (even an explanation which postulate "nothingness" or "non-being" as the best explanation) is better than an explanation based on God. Therefore, it is hard to see what evidence would count to them as positive evidence for God, because "nothing" will always be, for atheists, an available and better candidate to explain whatever phenomenon, fact or event mentioned by the theist as evidence of God's existence.
In God vs Nothingness as the only explanatory choices, atheists will prefer Nothingness...
Astonishing, indeed! This tell us a lot about the psychology and spiritual nature of atheists, and how far they're disposed to get in order to deny God's existence.
I consider Oppy to be a serious, brilliant, honest philosopher. But it is dissapointing to see him to appeal to any possible cavil or objection in order to block a conclusion favorable to theism, even when the conclusion derives from premises which are more plausible than their negations (and that atheists only deny when they're discussing arguments for God's existence).
That a serious, sophisticated philosopher like Oppy is forced to argue like that is more evidence for the intellectual weakness of contemporary atheism. This actually increases the confidence that the case for atheism is pretty weak.
Even lacking a proper or exhaustive analysis of efficient causation, we KNOW that efficient causation exists and produces the coming into being of things which begin to exist (including new biological species, new viruses, new diseases, new human beings, new cars, new computers, laptos, iphones and ipods, etc.). And no known and proven exception exists for the causal principle. This suffices to accept the causal principle as true (and as more plausible than its denial) and hence to accept that the unvierse has a cause (given the evidence for the universe's beginning).
Therefore, the kalam argument is an argument which OUGHT to be accepted by reasonable, scientifically well informed people, and hence meets Oppy's criterion of a successful argument.
What more reasonable evidence could an honest, open-minded, truth-seeking atheist to ask?