Assuming, from the title, that you're looking for argument by counterexample...
The obvious reply would be to invoke Godwin's Law - there's a quote in Mein Kampf along the lines of "I am convinced that by fighting off the Jews, I am doing the work of our creator...". Comments like this pretty reliably generate a response something like "Hitler was a diseased mind/insane/evil!" to which you may reply "Yeah, but he was pretty sharp, too." However, this has the downside of invoking Nazis, which in a certain kind of person may provoke an instant "This is a reactionary idiot" response and a complete discarding of the argument. So it's a temperamental trick, and I'm not skilled enough in the dark arts to know if it's a net gain.
On the other hand, you might prefer Pol Pat, or Ted Bundy, or any of a very large number of dictators and serial killers who don't produce the same mindkilling response as Hitler.
A lot of fictional evidence comes to mind as well, but we do try not to generalize from that... Still, if you just want to WIN the argument rather than win rationally, it may help to pull an example from some media form that the audience is likely to appreciate. Lex Luthor, Snidely Whiplash, Yagami Light (or L, if you prefer), Mephistopheles (or Faust), and so on.
Is that the sort of thing you wanted?
Hitler also had a lot of false beliefs about Jews.
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.