You can have some fun with people whose anticipations get out of sync with what they believe they believe.
I was once at a dinner party, trying to explain to a man what I did for a living, when he said: "I don't believe Artificial Intelligence is possible because only God can make a soul."
At this point I must have been divinely inspired, because I instantly responded: "You mean if I can make an Artificial Intelligence, it proves your religion is false?"
He said, "What?"
I said, "Well, if your religion predicts that I can't possibly make an Artificial Intelligence, then, if I make an Artificial Intelligence, it means your religion is false. Either your religion allows that it might be possible for me to build an AI; or, if I build an AI, that disproves your religion."
There was a pause, as the one realized he had just made his hypothesis vulnerable to falsification, and then he said, "Well, I didn't mean that you couldn't make an intelligence, just that it couldn't be emotional in the same way we are."
I said, "So if I make an Artificial Intelligence that, without being deliberately preprogrammed with any sort of script, starts talking about an emotional life that sounds like ours, that means your religion is wrong."
He said, "Well, um, I guess we may have to agree to disagree on this."
I said: "No, we can't, actually. There's a theorem of rationality called Aumann's Agreement Theorem which shows that no two rationalists can agree to disagree. If two people disagree with each other, at least one of them must be doing something wrong."
We went back and forth on this briefly. Finally, he said, "Well, I guess I was really trying to say that I don't think you can make something eternal."
I said, "Well, I don't think so either! I'm glad we were able to reach agreement on this, as Aumann's Agreement Theorem requires." I stretched out my hand, and he shook it, and then he wandered away.
A woman who had stood nearby, listening to the conversation, said to me gravely, "That was beautiful."
"Thank you very much," I said.
Part of the sequence Mysterious Answers to Mysterious Questions
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Basically, the question here is whether you can use the Dark Arts with purely Light intentions. In the ideal case, I have to say "of course you can". Assuming that you know a method which you believe is more likely to cause your partner to gain true beliefs rather than false ones, you can use that method even if it involves techniques that are frowned upon in rationalist circles. However, in the real world, doing so is incredibly dangerous. First, you have to consider the knock-on effects of being seen to use such lines of reasoning; it could damage your reputation or that of rationalists in general for those that hear you, it could cause people to become more firm in a false epistemology which makes them more likely to just adopt another false belief, etc. You also have to consider that you run on hostile hardware; you could damage your own rationality if you aren't very careful about handling the cognitive dissonance. There are a lot of failure modes you open yourself up to when you engage in that sort of anti-reasoning, and while it's certainly possible to navigate through it unscathed (I suspect Eliezer has done so in his AI box experiments), I don't think it is a good idea to expose yourself to the risk without a good reason.
An unrelated but also relevant point: everything is permissible, but not all things are good. Asking "is it okay to..." is the wrong question, and is likely to expose you to some of the failure modes of Traditional Rationality. You don't automatically fail by phrasing it like that, but once again it's an issue of unnecessarily risking mental contamination. The better question is "is it a good idea to..." or "what are the dangers of..." or something similar that voices what you really want answered, which should probably not be "will LWers look down at me for doing ..." (After all, if something is a good idea but we look down at it then we want to be told so so that we can stop doing silly things like that.)