Your ”friend“ is blackmailing you to profess religious faith. It’s an ages old pattern in our species.
One hypothesis is that he (subconsciously, perhaps) wants to protect against the Goodhart effect, i.e., you going against your stated ethics and then claiming “you never said murder was wrong.” Another hypothesis is that he has a coalition-forming mindset, where sides must be taken and rules followed. There are many more such just so stories we can dream up.
As you yourself know, people justify killing all the time. They just change the word. “Murder” is by its very definition an immoral kind of killing. What killings are societally acceptable obviously depends on the society in question and not some magical moral “truth.” Sam Harris’ analogy of moral landscapes (search for his TED talk for a short summary) is a good way to look at the validity of norms; They are “true” in so far as they create more net profits for a society that follows them relative to other normative systems. So killing terrorists is a celebratory event while killing random Joe just contracts the economy and undermines societal order.
My friendly advice to you is to not take people too seriously on debates on ethics. People prioritize signaling/reputation and norm enforcement over communicating their most objective thoughts. You’re much better served by judging their attitude via the actions they take. This is also true of oneself; Just having the right moral beliefs is worthless. What are you actually doing for others?
Pretty much anything can be right or wrong. It depends on the context. Murder is the deliberate killing of a human being in violation of the law. A French civilian killing an SS agent in 1943 constitutes murder, but is not an open-and-shut case of immorality.
The statement "murder is wrong" is too vague to assign a truth value to. It's like saying "chemistry is immoral". It depends what you're using it for.
As for confidences…
Confidences like 100% and 99.99% are not fundamental physical things like protons and photons. They're not even as concrete as cats and dogs. Confidences are abstractions created by people to make sense of the world we inhabit. A useful first step to unconfusing your disagreement with your friend might be to define exactly what you mean by "confidence".
There are different conceptions of what it means to be "right" or "wrong", and it's pretty easy to move uncertainty around so that parts of a moral evaluation CAN be 100%, while remaining less than 100% for any given fact behind the judgement.
An easy example: murder is 100% wrong, BY DEFINITION of "murder". If it's not wrong, it's not murder. But that just moves the uncertainty to "was this specific act murder"?
If you want to claim that nothing is 100% true, how do you react to "1 + 1 = 2"?
Recently, I had a discussion with a close friend about morality and, let us say, fundamentals of epistemology. This person has no connection to the aspiring rationalist community.
We started out talking about discussion norms. I had sent my friend Julia Galef's talk on scout mindset. In previous discussions, I had gotten the impression that my friend argued to persuade, and I argued to learn something. This had collided and some of these discussions had seemed quite unfruitful to me.
My friend agreed that in factual discussions, scout mindset is the way to go. In moral discussions, my friend argued that one tries to persuade as one is a 100% sure of their moral beliefs. This got me wondering. For a long time, I have held a vague belief that there are no 0s and 1s when it comes to holding true beliefs. I pointed out that I do not think that morality belongs in another category. My friend confronted me with asking how I could say that I am not a 100% sure that murder is wrong. Well, I said, I am like 99.99% sure that it is wrong. Here the discussion got a bit emotional. They said they would not want to be friends with someone who gives even a slight chance that murder, racism, homophobia or any other bad thing might be morally right.
To me, saying I am 99.99% sure feels almost the same as saying I am 100% sure. I just thought that it is not a good idea on principle to assign 0% or 100% to any belief. Many people have been wrong about moral issues in the past, so who am I to be so sure about them.
So, people of Lesswrong, how sure are you that murder is wrong? Are you 100% sure? How would you go about solving the disagreement with my friend?