"What we're reasonably sure is settled truth" does not necessarily equal truth. Nor does it necessarily equal "what we will want to believe once we know more".

Absolutely, which is what makes building in the ability to self modify so intrinsically important. The function of any ritual like activity shouldn't be any where near the vicinity of the "research arm" of the rationality community. Nothing should be acquired within them, nor determined through them. They should be about reinforcing the settled science, to minimize the amount of falseness that enters into the canon (I should point out, to be clear I'm using this term tongue in cheek). And for what does, something built around the Litany of Tarksi still allows for self modification.

And yes, any and all rationalists should be far enough along that they've developed a certain immunity to the process. That in and of itself makes no difference. Doing these types of things does measurable things to the brain, just as prayer/meditation do. The details are arbitrary; it doesn't matter if you're sacrificing a virgin, eating a wafer, or lighting a candle. What matters is doing the same thing as your fellow tribe members to build/maintain a sense of community. The proposition here is to simply replace the incorrect proclamations of how the universe works with correct ones. Instead of proclaiming Jesus Lord and Savior, you're proclaiming the map is not the territory and that your desire to know what is true is actually true (so if it turns out that the map IS the territory, then out it goes from the hymn book).

And the rationalist has the added (and important) benefit that no matter how much they give themselves over to the emotions of whatever ceremony, once they walk back out to the parking lot, their level headedness will return. The rationalist can walk out and think, "That sure was fun, but I understand what was happening and can safely put that suspension of rationality back on the shelf." In a way the Catholic can't (consciously) do when walking out of Mass.

So I disagree, I think these kinds of things, with effective substitutions of content, won't make us weaker to this form of manipulation, but rather stronger. Ultimately, when we cross the Singularity, we probably won't need these kinds of mind hacks anymore, but in the interim, I think they'll end up being quite important.