Don't know why you keep on getting downvoted... Anyway, I agree with you, in that particular case (not naming names!).
But I've seen no evidence that competence in designing a powerful AI is related to competence in controlling a powerful AI. If anything, these seem much less related than you'd expect.
I suspect Lumifer's getting downvoted for four reasons:
(1) A lot of his/her responses attack the weakest (or least clear) point in the original argument, even if it's peripheral to the central argument, without acknowledging any updating on his/her part in response to the main argument. This results in the conversation spinning off in a lot of unrelated directions simultaneously. Steel-manning is a better strategy, because it also makes it clearer whether there's a misunderstanding about what's at issue.
(2) Lumifer is expressing consistently high confidenc...
A stub on a point that's come up recently.
If I owned a paperclip factory, and casually told my foreman to improve efficiency while I'm away, and he planned a takeover of the country, aiming to devote its entire economy to paperclip manufacturing (apart from the armament factories he needed to invade neighbouring countries and steal their iron mines)... then I'd conclude that my foreman was an idiot (or being wilfully idiotic). He obviously had no idea what I meant. And if he misunderstood me so egregiously, he's certainly not a threat: he's unlikely to reason his way out of a paper bag, let alone to any position of power.
If I owned a paperclip factory, and casually programmed my superintelligent AI to improve efficiency while I'm away, and it planned a takeover of the country... then I can't conclude that the AI is an idiot. It is following its programming. Unlike a human that behaved the same way, it probably knows exactly what I meant to program in. It just doesn't care: it follows its programming, not its knowledge about what its programming is "meant" to be (unless we've successfully programmed in "do what I mean", which is basically the whole of the challenge). We can't therefore conclude that it's incompetent, unable to understand human reasoning, or likely to fail.
We can't reason by analogy with humans. When AIs behave like idiot savants with respect to their motivations, we can't deduce that they're idiots.