In 2012, a number of well-known scientists and philosophers gathered for a weekend to discuss hot-topics or unresolved issues within naturalism. Basically they were trying to scope out and/or develop a more coherent world-view from a strictly scientific/materialist perspective. The entire series is still available online and worth watching if you missed it.
One video is dedicated to their discussion of morality. To my surprise Steven Weinberg, a physicist, presented a solid argument against so-called science-based moral theories. His portion begins about 7 minutes into the video, and he remains pivotal to the remaining discussion.
The reason I found it so surprising is that he is not a philosopher himself, in fact he is usually critical of philosophy, and yet puts forward what I believe to be the most coherent philosophical analysis of morality from a naturalist perspective. What made it more surprising is that other philosophers I have a great respect for (Daniel Dennett and Massimo Piggliucci) did not seem to accept his arguments.
In short, Weinberg argues that science is not capable of generating moral "postulates" (rules), and so morality cannot be grounded in science or reason. Science and reason might be used to understand or elucidate the moral beliefs held by oneself or others, but they cannot be used to create or deliver beliefs you do not already have within you. This fits well with Hume's position on morality as I describe in my reply to Sam Harris. In fact, Weinberg mentions Hume in making his argument.
Weinberg's criticisms effect all normative moral theories, whether consequentialist (results determine the rightness of an act) or non-consequentialist (something is right/wrong independent of results). In response to this criticism, Massimo Piggliuccci introduces a different type of moral theory known as virtue ethics, which he explores in his own work. It differs from the first two moral theories by not focusing on delivering set moral rules regarding actions (simple right/wrong), but deliberating on what kind of life is worth living and so what habits might be useful to get there (virtues).
I became a bit confused with Piggliucci's description of virtue ethics, as he appeared to be claiming that it could be founded in science and reason. I tend to consider myself a virtue ethicist, or some form of such, and do not see how it counters Weinberg's criticisms. If anything as a virtue ethicist, I agree with Weinberg almost completely. Deliberations on a valuable life will rest on personal, subjective, irrational feelings. On a side note, I also disagreed with Piggliucci's equating loyalty with xenophobia or distrust of others. Loyalty is a positive feeling toward something and does not require any negative feeling toward anything else. Usually others (outside the group one holds loyalty to) are treated with indifference and not antipathy. These problems suggests future discussions I would like to have with Piggliucci.
More important, many of the attendees described the existence of an objective moral progress which they attribute to science/reason. While individual rights within legal systems have generally been expanding (though there have been reversals), and there may be decreases in crime as a result of many different societal factors, there is no evidence for an increase in morality among human populations. Even if there was progress, how can this be linked to science and reason when most of the world (including the west) is largely dominated by religious belief? Two of their key markers of moral progress (the rights of racial minorities and a single sexual minority) came at a time of expanding religious and nonscientific thinking within the US. I am not stating this as a defense of religion. I am just pointing out that it is hard to link science and reason to those legal achievements (if one can use law as a sign of moral progress). This would seem to have been more of an emotional or social than rational or empirical journey.
It has been a couple of years since that meeting, and I am interested whether any of the attendees have moved in one direction or other on this topic. Personally, I was delighted to hear Weinberg's account of how he moved from one moral theory to another, before abandoning normative ethics for a more descriptive understanding of human morality. Perhaps some have begun making a similar journey!