We seem to be dismissive of truths that can emerge outside of the realm of science and the scientific process. Anything related to morality seems to be dismissed as not true or false because there's no scientific objectivity to it.
I have great respect for Sam Harris and I would recommend his book The Moral Landscape to anybody. Still, among many errors that I think he made, two stand out to me: 1) he tries to extract and ought from and is and, 2) he tries to use science as a baseline for discovery of moral truth rather than just a component.
To make a messy summary of a 300 page book, Harris argued that objective moral truth and falsehood exist in a secular world. I agree with him there. We need to agree with him there (more on that later). The first problem is that he utterly fails to dismiss the deontological component which is necessary for his argument. I don't see how you construct a consequentialist set of moral values which presupposes the well-being of conscious creatures and that that well-being can be measured through science without explaining why anyone should care about well-being or science. How do you scientifically prove to a person that he or she should care about science?
I still view Harris as extremely helpful being that so many people on the secular left try to outright reject the concept of objectively correct or false moral values; but, his perspective is a fancy mansion built upon very wet sand.
Jonathan Rauch wasn't trying to hack at the core of moral values in his book Kindly Inquisitors; but, I think he struck the right chord. He took the opposite approach that Harris did - treat moral values as a subject of open inquiry, like science. Still, the physical and the metaphysical and the logical - just about every dissent, should be welcome. State whichever value you wish to state and be ready to subject yourself to criticism from checkers of all shapes, sizes, communities, etc. and we'll see what sticks and what doesn't.
This is a stronger approach than Harris's simply because the process doesn't narrow the window of acceptable inquiry.
Just start with the reality of opinions. Science doesn't deal with opinions outside of what can be physically tested. Moral values are opinions.
Harris's argument falls apart when he talks about measuring well-being because he fails to address the opinion that he has that that's the right measure of moral value. He has the same blind spot as most people who buy into scientism.
The reality is that we can actually be more sure of some things out of sheer logic while not needing science. Hell, mathematics is a discipline of logic, not science.
Can an opinion be wrong?
Of course it can.
"In my opinion, opinions can be wrong."
Try to refute that statement. You either believe that my opinion is right or at least reasonable; or, you have to tell me that my opinion that opinions can be wrong is wrong which would make the statement right because you're telling me that my opinion is wrong.
If opinions can be right or wrong and moral values are opinions, it's a steep uphill climb to show that moral values can't be right nor wrong.
It doesn't take the scientific method to show the objective moral truths that murder, rape, and theft are wrong. We all know this at some level. A person can genuinely believe that he was entitled to sex and another person could have entirely resisted his attack - we eventually have a third party come in and say, "Fuck you rapist, you should live in a cage for a while." There you go - that's a component of moral objectivity.
Sure, it's a social construct. So is language. That doesn't mean that there's no truth nor meeting of the minds nor objectivity in language. Orders aren't invalidated just because they're emergent. Truths don't become less true when they come from the bottom to the top rather than from the top to the bottom.
Yes, the idea of moral relativism should be a component in our debates; but, those arguments need to be regarded as fringe ideas. If you truly believe that no moral views can be objectively true or false, you have no reason to voice a moral opinion - ever. Even voicing your opinion that I'm wrong for saying that one moral value is superior to another is defeating your own supposed worldview.
Still, the point is that we need to embrace a system of moral inquiry whilst jettisoning a sense of moral certitude. We need to stop thinking that we know everything just as badly as we need to stop thinking that there's nothing to know.