I don't see how you can think that saying "humanity can someday find a way to build such a machine" isn't assuming the conclusion. That's the conclusion, and it's being used as an argument.
That is making commentary on the conversation with implied criticism of the other's perceived misuse of semantic quibbling.
"[Y]ou seem to have a concept of 'intelligence' that's entangled with many accidental facts about humans" is the conclusion. Slepnev assumes it. Therefore, Slepnev assumes the conclusion. (It would be a restatement of the conclusion if his earlier arguments hadn't also just been assuming the conclusion.) That the assumption of the conclusion is only implicit in the criticism doesn't make it any less unjustified; in fact, it makes it more unjustified, because it has overtones of 'the conclusion I have asserted is obviously correct, and you are stupid for not already having come to the same conclusion I have'.
Remember, I mostly agree with Slepnev's conclusion, which is why I'm especially annoyed by non-arguments for it that are likely to just be turnoffs for many intelligent people and banners of cultish acceptance for many stupid people.
One of the most annoying arguments when discussing AI is the perennial "But if the AI is so smart, why won't it figure out the right thing to do anyway?" It's often the ultimate curiosity stopper.
Nick Bostrom has defined the "Orthogonality thesis" as the principle that motivation and intelligence are essentially unrelated: superintelligences can have nearly any type of motivation (at least, nearly any utility function-bases motivation). We're trying to get some rigorous papers out so that when that question comes up, we can point people to standard, and published, arguments. Nick has had a paper accepted that points out the orthogonality thesis is compatible with a lot of philosophical positions that would seem to contradict it.
I'm hoping to complement this with a paper laying out the positive arguments in favour of the thesis. So I'm asking you for your strongest arguments for (or against) the orthogonality thesis. Think of trying to convince a conservative philosopher who's caught a bad case of moral realism - what would you say to them?
Many thanks! Karma and acknowledgements will shower on the best suggestions, and many puppies will be happy.