John McTaggart was a brilliant atheist who wrote a sustained attack on Christianity (Some Dogmas of Religion). I'm going to comment on his attempted attack on miracles:
There remains the argument that certain dogmas should be accepted because they have been held by men, or beings incarnate in human bodies, who have worked miracles, including the miracle of predicting the future.
A miracle is an event which we cannot explain by any natural law known to us, and which is therefore attributed, by the believers in its miraculous character, either to a special divine interference with the course of nature, or to the action of some law, differing in its nature from those which explain non-miraculous events. It is then argued that the occurrence of such events at the will of, or in connexion with, a particular being, is evidence, either that that being is himself divine, or that he enjoys special divine favor, and, in either case, that his teaching on matters of religious dogma is trustworthy.
Generally, a miracle is not attributed to divine agency simply by default. In addition, it may be in answer to a prayer to the God in question. Or a prophet may predict a miracle in God's name. There are indicators of the source over and above the fact that no natural process can explain it.
The evidence for the existence of miracles is an inquiry beyond our purpose. But we may remark in passing that, as Hume has pointed out \ if miracles are to be accepted as evidence of the truth of a religion, then whatever evidence there is for the miracles of one religion is evidence against the truth of all incompatible religions. There is perhaps no reason, if there are miracles at all, why they should not occur in connexion with several incompatible systems. There might be reasons why a God should work miracles in connexion with a false religion. Or again the miracles of all the systems except one's own might be ascribed, as they used to be ascribed, to devils. But then miracles would prove nothing about the truth of a religion. If, on the other hand, they can prove anything about it, then none but a true religion can have miracles connected with it Of two religions with incompatible dogmas, one, at least, must be false, and therefore only one, at most, can have miracles connected with it. Thus neither religion can be proved true, without disproving the existence of the miracles of the other religion. And in so far as these latter are at all probable, they render the truth of the first religion improbable.
i) Even if that objection were true, miracles would still contribute to a cumulative case for Christianity by eliminating naturalism from consideration.
ii) In addition, the objection is overstated. For instance:
Supposing that miracles were proved to exist, and to exist in connexion with one religion only, should we be entitled to believe that religion to be true? It seems to me, to begin with, that the existence of the miracle would not prove that it was due to the action of God — meaning by God a supreme being. The amount of power required for any miracle, however startling, can never be proved to be more than finite. And in that case it is always possible that it should have been performed by some being whose power, while much greater than human power, might be far below the power of a supreme being.
i) Even assuming that's so, if miracles take naturalism off the table, then that makes a very significant contribution to the overall case for Christianity.
ii) It's not as if any single argument or line of evidence must prove Christianity at one stroke. It can be a process of elimination. If miracles eliminate naturalism, there are other arguments that eliminate religious alternatives to Christianity.
iii) McTaggart acts as though it's necessary to conclusively rule out any alternate explanation, yet that sets the bar far too high. Take a crime scene. Homicide detectives conclude the victim was killed by the jealous boyfriend of a woman he slept with. They have incriminating evidence on the boyfriend.
But suppose the victim was actually killed by the CIA because he discovered a sensitive military secret or because he had embarrassing information on a high-ranking government official. The CIA framed the boyfriend for the crime, planting false evidence. Or maybe the victim was killed by a race of sadistic extraterrestrials who like to toy with humans.
Suppose we can't disprove these alternate explanations? So what? There are many things we can't absolutely prove or disprove. The question is who is the best candidate to explain the phenomenon. It isn't necessary or reasonable to demand that we rule out every conceivable explanation. McTaggart has a double standard when it comes to Christianity. He has a highly artificial and inhuman standard for proving Christianity which no one reasonably applies to host of other issues. Admitted, McTaggart's own position (metaphysical idealism) was pretty esoteric. But that's a weakness.
If then a miracle were due to the action of such a superhuman but non-divine being, would it give any reason to suppose the religion to be true ? I see no reason to believe that a being who can raise the dead, or prophesy the future, or assist a man to do these things, would be a specially trustworthy guide on matters of religious dogma. The power of influencing the course of events, and the power of apprehending religious truth, are not always closely connected. Napoleon greatly excelled the average English clergyman in the first, but it would be a rash inference that he excelled him in the second.
Once again, it narrows the range of options to supernatural explanations.
Waiving this difficulty, and assuming that the miracle could prove the special interference of the supreme being, so that the religion connected with it could be accepted as his revelation, should we then be safe in accepting it as true ? We should not be justified, I submit, unless we had previously proved that the supreme being was good. For we have no reason to suppose that he will tell us the truth except that it would not be a good act to deceive us. If he is indifferent to the good, or if he is positively malignant, he may well tell us lies, either from caprice or in order to gratify his malignancy.
It is obviously impossible to trust to the revelation to tell us that he is good, since we have no reason to trust the revelation at all unless we know that he is good. This goodness must be proved independently. And thus one of the most important of dogmas cannot be proved by a miracle-based revelation.
If, however, this dogma has been independently proved, are we then entitled to accept the divine revelation as true ? Even then I do not think that we can do this. A God — that is, a good supreme being — will doubtless regard deceit as an evil. But there is, beyond doubt, much evil in the universe, and, if we are satisfied that there is a God, we must regard that evil as in some way compatible with his goodness. And then why not that further evil of a misleading divine revelation? If, for example, we attribute the existence of evil to God's limited power, and say that cancer and plague exist because they are the best that God can do for us under the circumstances, how can we be sure that the best thing he can do for us under the circumstances is not to deceive us about religious dogma? How can we be sure, for example, if God tells us we are immortal, that it is not a deceit — bad in itself, but good as the means of avoiding some greater evil?
i) These are variations on the Cartesian demon. If, however, a malevolent or universally deceptive deity exists, that's no less a problem for atheists than it is for Christians. That would be a defeater for both. Why does McTaggart imagine the onus lies on Christians to disprove this thought-experiment? His own position falls prey to the same hypothetical.
ii) How seriously should we take thought-experiments designed to establish global skepticism? The fact that human imagination can dream up hypothetical traps from which we can't escape may be an entertaining intellectual diversion, but no reasonable person bases his belief or behavior on such fanciful scenarios. These are mental tricks. Their main value is to demonstrate the limits of what can be proven or disproven. But proof and knowledge are not equivalent.
iii) What's the point of asking whether we might be hopelessly deluded? If we are hopelessly deluded, then posing such questions won't lead to enlightenment. Indeed, on that view, skeptical thought-experiments are one of the ways in which the Cartesian demon toys with us. It's just another blind alley in the nautilus shell of the global illusion.