"Morality and values depend on the existence of conscious minds—and specifically on the fact that such minds can experience various forms of well-being and suffering in this universe. Conscious minds and their states are natural phenomena, fully constrained by the laws of the universe (whatever these turn out to be in the end). Therefore, questions of morality and values must have right and wrong answers that fall within the purview of science (in principle, if not in practice). Consequently, some people and cultures will be right (to a greater or lesser degree), and some will be wrong, with respect to what they deem important in life."
The crux of your main tenet is that: “morality... depends on the... fact that [conscious] minds can experience various forms of well-being.” This is only one reduction in terminology away from being completely circular. Since morality is defined as “principles concerning the distinction between right and wrong or good and bad behavior,” morality and ethics are, in other words, simply “rules for acting well.” Substituting this definition of morality into your main statement, you get the fact that: "acting well... depends on the... experience of well-being. This is tautologically correct, but it’s uninteresting without anchoring the subjective adjective well to some objective fact. Without that anchor, the circular definition spins in place with nothing to grip, and the relativists and nihilists are free to point out that you are simply constructing a floating argument based on socially agreed upon definitions. The anchor we’ve been looking for though has been staring us all in the face for 150 years.
In one of my previous jobs in management consulting, I was a Special Advisor to the Director of the U.S. Secret Service and was tasked with helping him revise the performance metrics for his agency. Essentially, the main measurement that Congress used to evaluate the performance of the Secret Service was whether or not the president was alive. This was a binary, yes or no, easy to measure outcome of all the work the Secret Service does, but it told us nothing about whether the agency was getting better or worse at achieving this outcome. Was the president well-protected or getting closer to becoming unprotected? No one could say. The best practice for solving this type of problem in complex organizations is something called a balanced scorecard, where you measure performance across the entire value chain of the organization and look for problems in the system. You choose what measurements to take on the way from inputs, through internal processes, to outputs, and finally outcomes, and then you define targets in each area that will lead you to reach your desired (or congressionally mandated) outcomes. In this example, having a well-protected president was necessary, but it was only a subjective output of the agency. In The Moral Landscape, the well-being of conscious creatures is similarly just an output in the system—in this case, the system of life that is regulated by the internal processes of our moral rules. Using another example you like to cite, health is merely a subjective output in the system of medicine. However, the objective reason we know the Secret Service has not failed is because the president has not died. The objective reason we know the doctor has not failed is because the patient has not died. The objective reason we know our morality has not failed is because our species has not gone extinct. These are the objective outcomes that anchor the subjective evaluation of the rest of the processes. Russell Blackford was right to be looking for a metric to validate your claim; you were just pointing him in the wrong direction to find it. You ask in your book if the worst possible misery for everyone is not the worst possible outcome for a universe, but a universe devoid of life, devoid of any hope for well-being, is an even worse outcome.
Let me pause here to explain that I am not advocating the naturalistic fallacy of a eugenicist or the naïve adaptivism of a relativistic anthropologist. There is a difference between existing and surviving. It appears to us, for example, that sharks are surviving because they have been around for millions of years. Endangered pandas, on the other hand, are likely (though sadly) just existing at this moment in time. Based on what we know from evolutionary studies, some species endure and some species wink in and out of existence based on some rather clear properties: adaptability, diversity, redundancy, robustness, habitat stability, etc. Further, we humans are thriving in our survival because of the progress that comes from cooperation, which, as you note, come from: “kindness, reciprocity, trust, openness to argument, respect for evidence, impulse control, the mitigation of aggression, fairness, justice, compassion”, etc. Actions of these types would all be categorized as internal processes in the balanced scorecard method I outlined above—necessary, but also not sufficient to describe the successful performance of our species in this universe.
In the future, evolutionary studies could guide a science of morality towards understanding which actions meet the objective root-cause goal of survival. At present, we already know from scientific investigations into the consilient fields of biology that these actions take place over fantastically long timelines and are enmeshed in incredibly intricate webs of support, so we would be extremely arrogant to think we may ever know the full consequences of our behaviors. Morally tricky areas are tricky precisely because of this kind of epistemic opacity. Using a non-tricky point to prove the existence of the rule though, I believe you are right to say that it is obvious the Taliban is not leading a moral society, but this is because they are not leading a society that is progressing towards survival. (How would they deal with the asteroid strike that is likely to come one day?) That is the objective reason, discovered by science, that their morality is not as good as, say, Denmark’s. The well-being of conscious creatures is a necessary subjective output along the way, but the long-term survival of life over evolutionary timelines is the peak objective outcome that sufficiently describes the moral landscape.