OOC - some examples would be nice :)

Well, whenever I open this topic, giving concrete examples is problematic, since these are by definition respectable and high-status delusions, so it's difficult or impossible to contradict them without sounding like a crackpot or extremist.

There are however a few topics where prominent LW participants have run into such instances of respectable opinion being dogmatic and immune to rational argument. On example is the already mentioned neglect of technology-related existential risks -- as well as other non-existential but still scary threats that might be opened due to the upcoming advances in technology -- and the tendency to dismiss people who ask such questions as crackpots. Another is the academic and medical establishment's official party line against cryonics, which is completely impervious to any argument. (I have no interest in cryonics myself, but the dogmatic character of the official line is clear, as well as its lack of solid foundation.)

This, however, is just the tip of the iceberg. Unfortunately, listing other examples typically means opening ideologically charged topics that are probably best left alone. One example that shouldn't be too controversial is economics. We have people in power to regulate and manage things, with enough power and influence to wreak havoc if they don't know what they're doing, whose supposed expertise however appears, on independent examination, to consist mostly of cargo-cult science and ideological delusions, even though they bear the most prestigious official titles and accreditations. Just this particular observation should be enough to justify my Titanic allegory.