This is an extraordinary claim by Eliezer Yudkowsky that progress is a ratchet that moves in only one direction. I wonder what, say, the native Americans circa 1850 thought about Western notions of progress? If you equate "power" with "progress" this claim is somewhat believable, but if you're also trying to morally characterize the arc of history then it sounds like you've descended into progressive cultism and fanaticism.
So, now replying knowing your context, this actually came up in discussion with Eliezer at the dinner after his talk at MIT. The most agreed upon counterexample was more restrictive drug laws. But if one interprets Eliezer's statement as being slightly more poetic and allowing that occasional slips do occur but that the general trend is uni-directional, that looks much more plausible. And the opinion of the general American population in 1850 in many ways doesn't enter into that: most of that population took for granted factually incorrect statements about...
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