No I don't believe that they are unknowable. Where did I say that?
OK, how can objective moral values be known? (Please don't say "EPISTEMOLOGY LOL" again...) I understand the idea of using harm objectively but I see no way that the outcome wouldn't be to at least some extent, subjective. I think all of us would agree that rape and murder cause harm and are therefore morally wrong, but what about the arguable harm of raising a child to have strong religious views?
You are talking about moral epistemology like so many of your friends. Objective moral values can exist regardless of whether I understand them or not.
But what practical use is that? I could say that I believe that there exists an absolute truth that a certain piece of music or art form is objectively better than others, but how could that be determined? It's impossible, and yes, I could still say I believe this absolute truth exists but if I don't know it and can't determine it, what's the point?
This is moral epistemology again. Everyone obviously doesn't adhere to the same thing. That doesn't affect in any way the ontological question of what is the foundation for objective moral values and duties.
I'm glad you agree that everyone doesn't adhere to the same thing. With that in mind, assuming your objective moral values exist, what good are they? What's the point of them? What purpose do they serve if they're not adhered to?
If you want to find out about moral epistemology then Google is your friend. It's a completely different topic.
It's intrinsically linked. If you want to believe objective moral values exist even though you don't understand them and they have no practical use to you or anyone else, that's up to you I suppose but it seems very strange.