[Question] Can you be 100% confident in your moral beliefs?

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?