When someone claims that science can answer moral questions, I want to know how they objectively arrive at those answers, how scientists address 'ought I?' without merely replacing priests as the arbitrary decider of what is good and proper, what is moral. There may well be proponents of such a move, prepared to argue that white coats are better than black robes when it comes to making stuff up, but I can't see that being supported by logic and reasoning, just by self- (and class-) interest.
It might help me, and others, appreciate your position if you could offer up a concrete example of what you consider to be a moral question, along with an explanation of how science (logic, reasoning) can answer it, without depending on a prior answer which has been plucked from the air. The mere absence of pretence that some omnipotent beardy gave you the prior answer is not enough to tempt me to follow the priests of science. If all there is are answers plucked from the air, I shall pluck them myself and science can focus on the things it actually can do.
Well, every time I try to logically show every step of the way, someone just goes up one level of abstraction again and asks "But how can science answer moral questions?" or "How can you derive an ought from an is?", just as if I've said nothing.
But very well, I can offer a concrete example this time if you think it will help, but I have to start from the beginning (otherwise people will claim that I am skipping an essential step). Let's make things very simple, because in practice moral questions are always unclear and it is hard (though not in principle impossible, as I attempt to show) to conclusively answer a moral question. Let's simplify by saying there are only three people, with simple desires:
Person 1 is a child who only cares about survival
Person 2 is the mother who only cares about the preferences of the child being satisfied.
Person 3 is the uncle, who cares equally about surviving and the preferences of the mother being satisfied.
We can distinguish here between selfish desires and altruistic or what you might call moral desires. The child is purely selfish. The mother is purely altruistic, but only with respects to the child. The uncle is more realistic as he has both selfish and moral desires, as a real person would. So how could morality flow from this?
Well, the mother could argue that the fairy in the sky dictates that children should always receive most of the food. This is a bogus argument because there is no such fairy, and as such the argument is based on nothing. The child could argue that he has constructed a moral axiom, that says that children should always receive most of the food because it is true a priori. This is a bogus argument because just saying something is an axiom or true a-priori proves nothing, and again there is no reason to favour this argument.
The uncle could try to be reasonable, and argue that each person is trying to satisfy their preferences regardless, and so it only makes sense to base the decision of what to do on those preferences. Based on the behaviour of the others, he can logically deduce what the preferences of each person are, in a process that is difficult in practice but not in any way merely a matter of opinion (preferences are facts, they are part of the physical universe like everything else in it). The mother could argue that she is satisfying the preferences of the sky fairy but she would be lying or deceiving herself (at least in this example, given the above). The preferences of each person are objective fact and the uncle can tell what they are. The uncle might therefore suggest that they all do away with pretence and work together to satisfy their desires instead. Once everyone is honest about what they want, the uncle agrees to give half of his food to the mother, who in turn gives all of her food to the child. This might go against the uncle's instincts, since he cares about the mother, but he accepts it since that is what the mother wants. Everyone agrees that this outcome is better at least compared to the alternative where everyone fights each other or argues each other to death.
Now hold on, I hear you cry. This is not a system of morality, this is three people agreeing to satisfy each others preferences! Well okay, but this is the basis for a moral society. A group of three people don't need moral rules because everyone knows each other. But what if more people arrive? Everyone has somewhat different preferences and it is hard to keep track of it all. So now it might be optimal to establish moral rules, guidelines or rules of thumb basically, that everyone agrees help satisfy the preferences of people in the group even though they can never do so perfectly. A rule might be established that says that children in general should receive more food/care, because there are a lot of mothers who strongly desire this, and a lot of uncles who wish for their sisters to be happy (even though they do not care for their nieces and nephews directly). A rule in general might be established not to hurt others. But what if psychopaths are introduced? Surely their desire to hurt others is not intrinsically worth less than other preferences? Well, no, because there is no such thing as "intrinsic worth" in the first place. Other people won't value that psychopath's preferences and moral rules won't take them into account, as long as the psychopaths are in the minority. In fact many might desire that they be killed outright, given that their preferences pose a threat to the preferences of so many others. But what if those psychopaths have mothers who value their well being? Well, in that case moral rules might be established that say that no, not even psycopaths must be killed, though their preferences may not otherwise be satisfied. As you can see, moral rules emerge.
So how does science enter into this? Well, if you have neuroscience you can read someone's mind and objectively establish their preferences, which might be really useful in creating more effective moral rules. More to the point, however, the fact that this is possible conclusively shows that preferences are part of the physical universe. Even in todays society, you still have people trying to claim the old trick where a fairy in the sky happens to have the same preferences as them. Or someone will claim in objective universal moral standards (which happens to be the same as the preferences of the person claiming this.) And often times it works, sadly, because people are gullible. But these claims are objectively bogus, since they are based on nothing. The only thing that is not bogus is moral rules based on people's preferences because guess what, that is the only thing that motivates people and therefore the only thing a society can be build on. Which means that my whole moral argument is based on what motivates people in reality, not what I feel ought to motivate people in principle, because I am not one the sky fairy charlatans trying to have my own preferences unduly maximised (as everyone here seems to accuse me off. I wonder why people evolved to be so suspicious of other people's moral and political arguments? Ahem...

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So yea, the whole thing I am claiming is that no, you can't just come up with a random moral system and call it as good as any, it has to be based on people's preferences or else nobody has reason to care. No, an argument based on sky fairies is not as valid as any other. No, morality is not arbitrary. Yes, the fact that you can measure people's preferences scientifically matters. Combine this with the fact that you can objectively determine (using science) which actions deliver which outcomes (deterministic universe and all that), and you arrive at the inevitable conclusion that there is only one best option for society to take, whatever that is. So no, you should not go around saying that it is all just opinion, anyway. The whole process is objective, even though it is based on people's preferences which do vary, because there simply is no bloody alternative.
So, yea, really long post. Maybe not what you were looking for when you asked for a concrete example. But bloody hell, what else am I supposed to do, when every post I make just results in the same old reply of "but you missed the first step". In fact, who wants to bet some guy still claims that I have not shown why people ought to care about preferences? Or how all morality is subjective because you can't convince a psychopath to care about someone else's preferences? I am not holding my hopes up, anyway.
P.s.: In replying to this lengthy post, please do not quote separate paragraphs and address them individually. Quote mining never leads to productive discussion in my experience, and in this case the reply would just get ridiculously long. Please address the whole argument in its entirety instead.