Again, I go back to Lewis on this. Lewis accepted the AFR against naturalism, and then accepted Absolute Idealism, which was extremely popular in his time. Then he found fault with Idealism and became a theist, and then finally a Christian. His argument against naturalism was a step on the way to theism, eliminating one of the major options. But he didn't take step into theism until later.
I am primarily concerned with what I would call the "great divide" between world-views for whom the mental is a basic cause, and world-views in which the mental is not a basic cause. If the AFR shows problems for the latter type of position, then I think the epistemic likelihood of theism becomes enhanced, as do all other "mentalistic" options.
I understand "naturalism" to encompass those world-views that are, at bottom, anti-mentalistic.
So we can distinguish two propositions:
A) The basic causes of the universe are mental in nature. They are inheretly perspectival, having a subject. They are inherently normative. Something being good or bad, or thought good or bad, has something to do with what goes on. They are intentional. What something is about makes a basic difference as to what happens in the world. They are also purposive. Purposes in human thought and action are not "skyhooks" that have to be analyzed out in favor of cranes. They are ground-level reasons why things happen.
b) What is fundamentally real is not inherently perspectival, is not inherently intentional, is not inherently normative, and is not inherently purposive. The appearance that these mental realities are operative in our world is a byproduct of biological evolution, and at the end of the day the skyhooks have to be replaced by cranes.
I have never said that you get theism automatically if the AFR is an effective argument for preferring A to B. When people point out non-theistic alternatives that are compatible with A, as if that were an answer to me, I have to say, with C. S. Lewis, "How many times does a man have to say something before he is safe from the accusation of having said exactly the opposite?"
In fact humans do not tend to respond positively to placebos. 70% or more of those taking them will not get better.
If 30% of those taking sugar pills will get better, then humans often respond positively to placebos. That's quite astonishing and fits well with other reasearch in psychology about the influence of positive thought about the future.
Actually, if one found out that they were taking a placebo they would want the real medicine and consequently increase their chances of survival.
I agree with this, but the point is that the placebo effect promoted survival in the past, not that it does now. Many traits don't serve survival well now but did so in the past (adrenaline in a stress situation).
But now you've jumped from an individual belief to a system of beliefs.
I agree that this is the best objection to the "systematic error" argument. I guess this could be turned into a good argument, but nobody has done this so far.
Natural selection does not select for individual beliefs. It selects for the mechanism which is capable of forming beliefs. A person whose brain is able to arrive at enough true beliefs to increase its chances of surviving the hazards of this dangerous world is, all else being equal, going to have a greater likelihood of passing on her genes than a person whose brain is less adept at good belief formation.
This is the typical answer to any argument from reason. I think the problem with this answer is that it requires and presupposes a huge metaphysical framework that is highly controversal and becomes less and less plausible. It requires the "naive" view of mental causation, the idea that the content of our thoughts directly influence behavior. David Chalmers has made a great case against the kind of mental causation required for this view.
Usually it also presupposes that evolution delivers an explanation for our phenomenological mental life. But this is highly implausible and disputed by many in the philosophy of mind. My zombie twin would have the same advante in natural selection that I have.
I can't make a cogent case against this objection in a comment here because it presupposes so much. But overall it seems to me that the premise of the objection is highly disputed and that contemporary philosophy of mind actually moves away from it. This makes the objection useless.
The reason why this objection is so common seems clear to me. It is very simple and fits very well with ordinary common sense convictions about the mental. This makes it attractive to anyone who is not familiar with the metaphysical problems it causes.