Here is Peter Kreeft's argument concisely --
Premise 1: Conscience has an absolute authority over me.
Premise 2: The only possible source of absolute authority is an absolutely perfect will, a divine being.
Conclusion: Such a being exists.
The version of Kreeft's argument Haywood chose to refute --
P1. Conscience has absolute, exceptionless, binding moral authority over us, demanding unqualified obedience.
P2. Only a perfectly good, righteous divine will has this authority and a right to absolute, exceptionless obedience.
C. Therefore conscience is the voice of the will of God.
Haywood then adds: (Note: the inescapable conclusion if P1 & P2 were true is that the conscience IS God. That should tell you right there how sound this argument is.)
False. To say that the conscience is the "voice of the will of God" implies a communication of knowledge between two beings. To say that my friend is the text message telling me what he wants is false. But if he were to mean, instead, that God is present to us in conscience, St. Thomas Aquinas writes in the Summa Q. 8, Art. 1:
I answer that, God is in all things; not, indeed, as part of their essence, nor as an accident, but as an agent is present to that upon which it works. For an agent must be joined to that wherein it acts immediately and touch it by its power; hence it is proved in Phys. vii that the thing moved and the mover must be joined together. Now since God is very being by His own essence, created being must be His proper effect; as to ignite is the proper effect of fire. Now God causes this effect in things not only when they first begin to be, but as long as they are preserved in being; as light is caused in the air by the sun as long as the air remains illuminated. Therefore as long as a thing has being, God must be present to it, according to its mode of being. But being is innermost in each thing and most fundamentally inherent in all things since it is formal in respect of everything found in a thing, as was shown above (Question 7, Article 1). Hence it must be that God is in all things, and innermostly.
Haywood continues:
P1 is false. Kreeft defines conscience to be that way, but admits that others do not. "The modern meaning tends to indicate a feeling that I did something wrong." That is the what we actually observe to exist. The rest is simply assertion. But included in his definition is that all humans have knowledge of an absolute obligation to holiness. I do not have knowledge of this obligation, therefore P1 is false.
Haywood hasn't proven the argument to be false, but has proven Kreeft's accusation of the modern man's definition to be true: that the modern meaning tends to indicate a feeling that I did something wrong. Haywood leaves out Kreeft's most accurate explanation of his point out: "[conscience] is first of all the knowledge that I must always do right and never wrong." This is what Kreeft meant by "obligation to holiness". Earlier in our debate, Haywood mentioned that it's unpleasant to consider that theists can't do right unless they believe in eternal punishment. It's a comment made often by atheists. But to do right, I must believe doing right is better than doing wrong. Or else, I must not consider doing wrong better than doing right. So I must believe that I should (obligation) do right and not (obligation) do wrong. They must also admit common moral facts, a knowledge of which things are right and which things are wrong. Only in particular circumstance do we have "feelings". The premise of the argument concerns the authority of conscience, not of the knowledge moral facts (which arouse what Haywood calls "feelings").
Haywood continues:
P2 is simply assertion. He "supports" it by adding the superfluous words "absolute" and "binding". Conscience isn't absolute. Different people have different moral intuitions; it's rare that two people agree. Conscience isn't binding. People are free to go against it, and billions do every day. Then they feel bad, because conscience is their feeling of what they should have done. No magic involved.
What Haywood calls "different moral intuitions" and when he says, "it's rare that two people agree", he's referring to moral facts rather than the "knowledge that I must always do right and never wrong". Kreeft explicitly stated the premise was not referring to moral facts, or "moral intuitions".
Conscience isn't binding.
"Must" is a pretty binding word.
People are free to go against it, and billions do every day.
Those that go against "the knowledge that [they] must always do right and never wrong" are those that do wrong because it's wrong. Masochists seek pleasure (a good) in pain. Psychopaths (antisocial personality disorder) seek good only for themselves, at the cost of all else. Many do evil to obtain a good end, but I want proof that "billions" do evil for its own sake "every day".
Then they feel bad, because conscience is their feeling of what they should have done.
If someone knows they are acting for evil's own sake, they don't feel bad after the fact, but before. It's called conscience (and this in the sense of moral facts). But if that person acted in good conscience (doing good for its own sake) but, reflecting on the consequences of their actions, saw that they were bad and feel guilty, still acted according to "the knowledge that [they] must always do right and never wrong".
There's no disproof here -- just a misunderstanding of what the premise is stating.
Haywood continues:
The conclusion is of course unproven, since it's based on false premises, but it's also absurd. Psychopathic killers clearly refute this argument, since they do not feel remorse. Their conscience, if they have one, is not binding on them.
Most people don't feel remorse for acting in good conscience. What's malformed in psychopaths is the moral facts of what's right and wrong, not the obligation to do what's right and avoid what's wrong.
Haywood continues:
Redefining "conscience" so that psychopaths follow a "conscience" that tells them they should murder leaves you with not only tautology, but absurdity:
At the top of this post, I put in bold "version" because Peter Kreeft, in stating the argument in that particular way, did so at the end of his article. It assumes that the conscience has been properly formed by the truth/moral facts:
"To sum up the argument most simply and essentially, conscience has absolute, exceptionless, binding moral authority over us, demanding unqualified obedience. But only a perfectly good, righteous divine will has this authority and a right to absolute, exceptionless obedience. Therefore conscience is the voice of the will of God.
Of course, we do not always hear that voice aright. Our consciences can err. That is why the first obligation we have, in conscience, is to form our conscience by seeking the truth, especially the truth about whether this God has revealed to us clear moral maps (Scripture and Church). If so, whenever our conscience seems to tell us to disobey those maps, it is not working properly, and we can know that by conscience itself if only we remember that conscience is more than just immediate feeling. If our immediate feelings were the voice of God, we would have to be polytheists or else God would have to be schizophrenic."
Therefore, if your conscience (in the sense of feelings I presume, since no moral fact says this to be good) tells you to murder, your conscience (knowledge of moral facts) is malformed.
The conclusion of Haywood's syllogism also presumes the authority of conscience, that somehow a psychopath would realize that murder is wrong (knowledge of moral facts) and shouldn't do it because his obligation is to what's right, not wrong. But if no such obligation to what's right exists (as Haywood claims), there's nothing to move the psychopath from not murdering. There's actually no reason to call someone a psychopath who simply does as they please. We all do, right?
If you say that genetics or abuse or evil spirits can alter what your conscience tells you what to do, then conscience is clearly not the voice of the will of an omnipotent God.
Regarding genetics, we don't say this can alter our conscience (obligation to do what's right).
Regarding abuse, it may alter our pursuit of truth by replacing the ability to reason with passion for revenge (which would be seen as a good, and imply our obligation to it), but that's still moral facts.
Regarding evil spirits, they can lie to us and often do. That's why we pursue the truth.
A note about "authority":
Authority isn't taken in the sense of the ability to forcefully control another, as if no free will existed. Rather, authority is taken in the sense that a physicist or chemist has authority in their field of study. Their authority comes from their knowledge of facts in regards to the physical world. However, they don't forcefully carry out any of the natural laws they articulate. So, why is it they are authorities? Because they are a reference to laws and facts.
A note about "authority":
Authority isn't taken in the sense of the ability to forcefully control another, as if no free will existed. Rather, authority is taken in the sense that a physicist or chemist has authority in their field of study. Their authority comes from their knowledge of facts in regards to the physical world. However, they don't forcefully carry out any of the natural laws they articulate. So, why is it they are authorities? Because they are a reference to laws and facts.
My conclusion to Haywood's refute is that he misunderstood what Kreeft meant by conscience, therefore didn't refute the argument.