I think you're going to have a very tough time defending this claim. You might have better luck, though, with a claim that ends up doing much the same work for the subject under discussion: right and wrong do exist, and every theory we humans have come up with so far is wrong by that purist standard. But some human theories are less wrong than others, and it's the "degree of wrongness" that matters, practically speaking.
I think you're going to have a very tough time defending this claim. You might have better luck, though, with a claim that ends up doing much the same work for the subject under discussion: right and wrong do exist, and every theory we humans have come up with so far is wrong by that purist standard. But some human theories are less wrong than others, and it's the "degree of wrongness" that matters, practically speaking.