I'm worried because, well, we in Less Wrong do buy into a particular grand narrative of progress.
I don't know in whose name you're speaking when you talk in first person plural. However, if I would have to point out one valuable insight from the whole of OB/LW, it's that the kind of progress that is considered the least controversial and problematic one nowadays, and which is hailed as uniformly beneficial by a strong consensus across the ideological spectrum -- namely, technological progress -- in fact likely has some nasty surprises in store for us.
On the other hand, technological progress is a matter of objective and measurable accomplishment, not some grand moral narrative. For the sort of example you're looking for, you can consider any major social change in recent centuries that is considered a matter of enlightenment and moral progress nowadays.
Well, there have been many dead-ends in political evolution, but at the end of the day and all things considered and between one thing and another, one can say that:
I have found this most wonderful (if fairly lengthy) article, and thought you would enjoy having it brought to your attention.
It is so good, I think we should include it among the references in the "Politics is the Mind Killer" wiki page. But, before that, I submit it to you, and ask you: is there anything in this article that would warrant its exclusion from this site? I mean, besides the fact that it is about politics, and written by a notorious Social-democrat (And is that in itself grounds for exclusion?).