I'm not trying to argue that humans are completely unpredictable, but neither are AIs. If they were, there'd be no point in trying to design a friendly one.
About your point that humans are less able to predict AI behavior than human behavior, where are you getting those numbers from? I'm not saying that you're wrong, I'm just skeptical that someone has studied the frequency of girls saying hello to strangers. Deep Blue has probably been studied pretty thoroughly; it'd be interesting to read about how unpredictable Deep Blue's moves are.
Right. And I'm not trying to argue that we should despair of building a friendly AI, or of identifying friendliness. I'm just noting that the default is for AI behavior to be much harder than human behavior for humans to predict and understand. This is especially true for intelligences constructed through whole-brain emulation, evolutionary algorithms, or other relatively complex and autonomous processes.
It should be possible for us to mitigate the risk, but actually doing so may be one of the most difficult tasks humans have ever attempted, and is certain...
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.