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.
If it's only possible to deny that scientific theories are ever wrong by denying the very distinction between right and wrong, then I think that underlines my point. Freedom from being wrong at the price of never being right doesn't seem like a very good bargain.
As to the question of whether pragmatist theories of truth are viable, that is a separate one, but I tend to think that the standard objections are quite decisive.
Right. My entire claim is that right and wrong do not exist, only successful or unsuccessful.