Sounds like you've got the "things from the stars" story flipped - in that parable, we (or our more-intelligent doppelgangers) are the AI, being simulated in some computer by weird 5-dimensional aliens. The point of the story is that high processing speed and power relative to whoever's outside the computer is a ridiculously great advantage.

Yeah, I think the idea behind keeping the transcripts unavailable is to force an outside view - "these people thought they wouldn't be convinced, and they were" rather than "but I wouldn't be convinced by that argument". Though possibly there are other, shadier reasons! As for the encryption metaphor, I guess in this case the encryption is known (people) but the attack is unknown - and in fact whatever attack would actually be used by an AI would be different and better, so we don't really get a chance to prepare to defend against it.

And yep, that's another standard objection - we can't just make safely constrained AIs, because someone else will make an unconstrained AI, therefore the most important problem to work on is how to make a safe and unconstrained AI before we die horribly.