And you can't have a site like LessWrong, that talks about how to avoid errors that humans systematically make - because, like in the trolley problem case, you must claim they aren't errors, they're value judgements.

Even when holding a view that human values can't be improved, rationality techniques are still useful, because human values conflict with each other and have to be prioritized or weighted.

If value knowing the truth, and I also in the holistic sense "value" making the conjunction fallacy, then LessWrong is still helpful to me provided I value the first more than the second, or if the weighting is such that the net value score is increased even though the individual conjunction fallacy value is decreased.