Responding just to the title of the post, doesn't the simple question, "Is rationality teachable?" really boil down to:

"Is rationality a characteristic that is to a significant extent accessible to modification through behavioral means?"

And if you try on the answer, "Nope, it's pretty much all hardwired in," it seems pretty obviously ridiculous, so...

Is that a stupid answer?

(I mean, I guess you're not actually asking if rationality is teachable in strict theoretical principle, but: "Are we at lesswrong really doing anything to cause a significantly greater increase in the rationality of our members from where they were when they came to us than would have obtained anyway if they hadn't found us?")