The problem with "Act on what you feel in your heart" is that it's too generalizable. It proves too much, because of course someone else might feel something different and some of those things might be horrible. But if my epistemology is an appeal to an external source (which I guess in this context would be a religious book but I'm going to use "believe whatever Rameses II believed" because I think that's funnier), then that doesn't necessarily have the same problem.

'Act on an external standard' is just as generalizable - because you can choose just about anything as your standard. You might choose to consistently act like Gandhi, or like Hitler, or like Zeus, or like a certain book suggests, or like my cat Peter who enjoys killing things and scratching cardboard boxes. If the only thing I know about you is that you consistently behave like someone else, but I don't know like whom, then I can't actually predict your behavior at all.

The more important question is: if you act on what you feel in your heart, what determines or changes what is in your heart? And if you act on an external standard, what makes you choose or change your standard?

The problem with "Act on what you feel in your heart" is that it's too generalizable. It proves too much, because of course someone else might feel something different and some of those things might be horrible.

It looks like there's all this undefined behavior, and demons coming out the nose from the outside because you aren't looking at the exact details of what's going on in with their feelings that are choosing the beliefs. Though a C compiler given an undefined construct may cause your program to crash, it will never literally cause demons to come out of your nose, and you could figure this out if you looked at the implementation of the compiler. It's still deterministic.

As an atheistic meta-ethical ant-realist, my utility function is basically whatever I want it to be. It's entirely internal. From the outside, from someone who has a system where they follow something external and clearly specified, they could shout "Nasal demons!", but demons will never come out my nose, and my internal, ever so frighteningly non-negotiable desires are never going to include planned famines. It has reliable internal structure.

The mistake is looking at a particular kind of specification that defines all the behavior, and then looking at a system not covered by that specification, but which is controlled by another specification you haven't bothered to understand, and saying "Who can possibly say what that system will do?"

Some processors (even x86) have instructions (such as bit rotate) which are useful for significant performance boosts in stuff like cryptography, and yet aren't accessible from C or C++, and to use it you have to perform hacks like writing the machine code out as bytes, casting its address to a function pointer and calling it. That's undefined behavior with respect to the C/C++ standard. But it's perfectly predictable if you know what platform you're on.

Other people who aren't meta-ethical anti-realists' utility functions are not really negotiable either. You can't really give them a valid argument that will convince them not to do something evil if they happen to be psychopaths. They just have internal desires and things they care about, and they care a lot more about having a morality which sounds logical when argued for than I do.

And if you actually examine what's going on with the feelings of people with feeling-driven epistemology that makes them believe things, instead of just shouting "Nasal demons! Unspecified behavior! Infinitely beyond the reach of understanding!" you will see that the non-psychopathic ones have mostly-deterministic internal structure to their feelings that prevents them from believing that they should murder Sharon Tate. And psychopaths won't be made ethical by reasoning with them anyway. I don't believe the 9/11 hijackers were psychopaths, but that's the holy book problem I mentioned, and a rare case.

In most cases of undefined C constructs, there isn't another carefully-tuned structure that's doing the job of the C standard in making the behavior something you want, so you crash. And faith-epistemology does behave like this (crashing, rather than running hacky cryptographic code that uses the rotate instructions) when it comes to generating beliefs that don't have obvious consequences to the user. So it would have been a fair criticism to say "You believe something because you believe it in your heart, and you've justified not signing your children up for cryonics because you believe in an afterlife," because (A) they actually do that, (B) it's a result of them having an epistemology which doesn't track the truth.

Disclaimer: I'm not signed up for cryonics, though if I had kids, they would be.

I'd have to disagree here; I think that "faith" is a useful reference class that pretty effectively cleaves reality at the joints, which does in fact lump together the epistemologies Penn Jilette is objecting to.

People who follow the moral code of the Bible versus peopel that don't is also a pretty clear criteria that separates some epistemologies from others.

The fact that some communities of people who have norms which promote taking beliefs on faith do not tend to engage in acts of violence, while some such communities do, does not mean that their epistemologies are particularly distinct.

People who uses a pendulum to make decisions as a very different epistemology than someone who thinks about what the authorities in his particular church want him to do and acts accordingly.

"faith-based reasoning is unreliable enough that it can justify anything, in practice as well as principle, including acts of extreme violence."

The kind of people who win the world debating championship also haave no problem justying policies like genocide with rational arguments that win competive intellectual debates.

Justifying actions is something different than decision criteria.

In what way is "deserve" a matter of fact?

If you're a moral realist, and you think moral opinions are statements of fact (which may be right or wrong), then you think it's possible to "know in your heart" moral "facts".

If you're a moral anti-realist (like me), and you think moral opinions are statements of preferences (in other words, statements of fact about your own preferences and your own brain-wiring), then all moral opinions are such. And then surely Manson's statement of his preferences has the same status as anyone else's, and the only difference is that most people disagree with Manson.

What else is there?

However, it's true that Jillette talks about factual amoral beliefs like fairies and gods. So my comment was somewhat misdirected. I still think it's partly relevant, because people who believe in gods (i.e. most people) usually tie them closely to their moral opinions. It's impossible to discuss morals (of most humans) without discussing religious beliefs.

Listening to their (own) hearts' is not empathy, it's just giving credibility to your instinctive beliefs, regardless of wether they have a basis or not.

I think that plenty of people who call themselves rationalists simply have no idea what listening to one's own heart actually means.

It's like talking with a blind man who has no concept about how green differs from red about how one using a traffic light, to decide when to stop your car. You mean at on time one lamp shown you that you have to stop and at another time it tells you to go ahead? How do you tell the difference?

How is believing that everyone is connected by a network of magical energy tethers and acting according to that any different than believing that my soul will be saved if I massacre 40 people and acting on that?

You basically left out the part about listening to your heart. Having a cognitive belief and making decisions based on mental analysis of the consequences of the belief is not what listening to one's heart is about.

If a human tries to murder another, certain automatic programming fires that dissuades the human from killing. Emotions come up. If you listen to them, you won't kill. You actually have to refuse to listen to your heart to be capable of killing. Maybe there are a few Buddhists who manage to be in a complete state of pure heartfelt love while they ram a knife into someone's else heart but that's very far from what 99.99% of the population is capable of.

In the military soldiers get trained to disassociate the emotions that prevent them from killing others. Psychopaths usually do have a bunch of beliefs about morals. What they lack is the ability to listen to their hearts in a way that guides their actions.

The philosophers of ethics steal more books than other philosophers. It's not clear that well thought out moral beliefs are useful for preventing people from engaging in immoral actions.

The only difference is the actual acts that you take due to the beliefs.

No. Whether or someone is in their head or listens to their heart can matter to the people around him, if those people are perceptive enough to tell the difference. It probably effects most people on an unconscious level.