1. Science can, in principle, answer moral questions even if it cannot do so in practice now.
2. The science that will answer these questions will be the rapidly advancing fields of brain, cognitive and, ultimately, consciousness studies.
3. The criterion on which these questions will be answered is "human wellbeing."
Now, I have nothing against wellbeing. Wellbeing is pretty nice. But somehow I don't think this criterion was determined scientifically. So yes, if we have a pre-determined criterion, science can certainly help us experiment to determine how to maximize it.
That said, I really don't see how this program is going to be very helpful. Indeed, I think you can see how this scheme has affected American politics for the worse. Let's raise taxes. Wellbeing of constituents goes down. Ok... let's cut services. Wellbeing of constituents goes down. What about the wellbeing of future generations? Fuck em. Similarly, we can look at the 'morality' of climate change. Maybe we can ask Sam Harris to measure the wellbeing of the people of 2050 and decide how to weigh that against the wellbeing of the people of today.
Something as simple as stealing becomes a problem. What if poor guy's wellbeing is increased more than yours decreases by being robbed by him? Sure, to deal with these situations, you can maybe jigger your definition of total wellbeing to make this work out the way you want it to, but to then say that science determined the answer is a complete sham. We're firing science arrows and then drawing targets around the one we want to be the right answer. There's nothing wrong with using some sort of rational process to come up with definitions of wellbeing (or right and wrong), but to somehow imply that the result of that process was just 'out there' waiting to be discovered is silly.
Seriously, if Harris came up with a wellbeing-o-meter and discovered that women who wear the burqa have higher self-esteem, less anxiety about their appearance, less frustration with choosing what to wear, experienced fewer catcalling incidents, and had more disposable income to spend on rearing their offspring, while experiencing signficantly reduced pleasure in the shaking what her mama gave her department. If he found that -- on balance -- their overall wellbeing was higher than that of non burqa wearing women...
would Harris say:
A) Often science contradicts our common sense ideas. I thought it was obvious that forcing women to wear the burqa reduced their wellbeing. However, I have discovered that such a strategy would maximize wellbeing. Thus, as an act in the interest of the public good, the scientific overlords have therefore passed such a law.
B) Clearly, the wellbeing formula needs to place higher numerical weight on the shaking what her mama gave her factor.(*) This is merely a simple recalibration of the universal objective wellbeingometer. It's technical.