To begin, I really like Stefan Molyneaux. He's helped me soldify my philosophic positions since I first started listening to his show.
However, this is regarding his ethics system of Universally Preferred Behavior.
The caller challenges Molyneaux's ethics system of Universal Preferable Behavior, but I think the guy was just not well spoken. Several of his points were weak, but I think the real crux of the conversation, and one I think that Molyneaux avoided, was the challenge, "How do arrive at the conclusion that what is preferable is what is moral?"
I find this interesting because, logically, I actually appreciate Molyneaux's work on UPB. However, he makes the leap that what is preferable is what is good, and I do not think that he has a proper justification for such a leap. It makes the core of his presup argument lose its validity. If we are simply a result of our biology, which Molyneaux argues early on in his book, then the consequences mean that what we find preferable is not what is good. It strikes me as a fit of philosophic convenience that he links the two, and an over-exertion to justify his libertarian principles, instead of a true justification.