Mike Huemer replies to his critics on Cato Unbound. My favorite part is his common-sense defense of common sense. His begins by methodically laying out the problem:
[T]he recommendation to "rely on common sense morality" is just another way of saying: "start from normative premises that seem obviously right to almost everyone." What is controversial about that? What else could someone say we should do? It seems to me that there are the following possible alternative views:
It is better to start from normative premises that seem doubtful or false, rather than ones that seem obviously correct.
It is better to start from normative premises that seem true only to some smaller number of people, such as perhaps the partisans of a particular ideology, rather than premises that seem true to almost everyone.
We may only use normative premises that seemed true to almost everyone throughout history, or across all human cultures.
We may only use normative premises that seem true to absolutely everyone.
We should start from no normative premises at all.
He then considers all five alternatives:
Alternatives (1) and (2) seem, well, obviously wrong.
Option (3) has one obvious problem: it leaves us with virtually nothing to work with. Or more precisely, those who object to my common sense moral premises on the grounds that they are not universal across cultures and times would have to say that almost nothing, perhaps nothing at all, is universal across cultures and times. So if (3) is to be a genuine alternative to my own methodology, (3) will have to be a methodology that is extremely unpromising, in the sense that it is extremely unlikely that any political philosophy could be supported using only the meager materials that this methodology sanctions. A defender of (3) might claim that the justified conclusion here is one of skepticism, rather than a rejection of the methodology. But let's be concrete here. I rely on premises such as "One should not physically attack, rob, kidnap, imprison, or enslave people, without having a good reason." Now, it might be objected that people in some cultures and some historical time periods in fact attacked, robbed, kidnapped, imprisoned, and/or enslaved people without having any good reason for doing so. Therefore, ... what? We don't know whether any of those practices were good or bad? It's illegitimate in a political argument to assume that attacking people for no reason is bad? It seems to me that if someone draws those conclusions, that person must be a moral skeptic, or close enough as makes no difference.
As I have suggested, option (3) is in danger of collapsing into (5). Option (4) collapses into (5) immediately: there is no moral premise that seems true to absolutely everyone, including psychopaths, the mentally disabled, primitive tribes, and Adolf Hitler.
So we come to option (5): use no moral premises. Since it is not possible to (correctly) infer moral conclusions entirely from non-moral premises, this option simply entails moral skepticism - we draw no moral conclusions at all. Now, some people think that is the correct result. But it is not my job to refute moral skepticism in a book about political philosophy, any more than it is the job of an author to refute skepticism about the external world in a book about physics. Political philosophy books are for people who accept that it is sometimes possible to say that something should or should not be done. If you reject that, then you don't have a problem with my book. You have a problem with the entire field of social and political philosophy.
Hasn't common sense been wrong before? Of course. But how do people show that a common sense view is wrong? By demonstrating a conflict with other views even more firmly grounded in common sense. The strongest scientific evidence can always be rejected if you're willing to say, "Our senses deceive us" or "Memory is never reliable" or "All the scientists have conspired to trick us." The only problem with these foolproof intellectual defenses is... that... they're... absurd.