Do you have any actual reason (introspection doesn't count) to "expect LWers to be the kind of high-NFC/TIE people who try to weigh evidence in a two-sided way before deciding"? [...] I'm requesting the raw original basis for the assumption.
LWers self-report having above-average IQs. (One can argue that those numbers are too high, as I've done, but those are just arguments about degree.) People with more cognitive firepower to direct at problems are presumably going to do so more often.
LWers self-report above-average AQs. (Again, one might argue those AQs are exaggerated, but the sign of the effect is surely right given LW's nerdy bent.) This is evidence in favour of LWers being people who tend to automatically apply a fine-grained (if not outright pedantic) and systematic thinking style when confronted with a new person or organization to think about.
Two linked observations. One: a fallacy/heuristic that analytical people often lean on is treating reversed stupidity as intelligence. Two: the political stupidity that an analytical person is likely to find most salient is the stupidity coming from people with firmly held, off-centre political views. Bringing the two together: even before discovering LW, LWers are the kind of analytical types who'd apply the reversed stupidity heuristic to politics, and infer from it that the way to avoid political stupidity is to postpone judgement by trying to look at Both Sides before committing to a political position.
Every time Eliezer writes a new chapter of his HPMoR fanfic, LW's Discussion section explodes in a frenzy of speculation and attempts to integrate disparate blobs of evidence into predictions about what's going to happen next, with a zeal most uninterested outside observers might find hard to understand. In line with nerd stereotype, LWers can't even read a Harry Potter story without itching to poke holes in it.
(Have to dash out of the house now but I'll comment on the rest soon.)
Making fun of things is actually really easy if you try even a little bit. Nearly anything can be made fun of, and in practice nearly anything is made fun of. This is concerning for several reasons.
First, if you are trying to do something, whether or not people are making fun of it is not necessarily a good signal as to whether or not it's actually good. A lot of good things get made fun of. A lot of bad things get made fun of. Thus, whether or not something gets made fun of is not necessarily a good indicator of whether or not it's actually good.[1] Optimally, only bad things would get made fun of, making it easy to determine what is good and bad - but this doesn't appear to be the case.
Second, if you want to make something sound bad, it's really easy. If you don't believe this, just take a politician or organization that you like and search for some criticism of it. It should generally be trivial to find people that are making fun of it for reasons that would sound compelling to a casual observer - even if those reasons aren't actually good. But a casual observer doesn't know that and thus can easily be fooled.[2]
Further, the fact that it's easy to make fun of things makes it so that a clever person can find themselves unnecessarily contemptuous of anything and everything. This sort of premature cynicism tends to be a failure mode I've noticed in many otherwise very intelligent people. Finding faults with things is pretty trivial, but you can quickly go from "it's easy to find faults with everything" to "everything is bad." This tends to be an undesirable mode of thinking - even if true, it's not particularly helpful.
[1] Whether or not something gets made fun of by the right people is a better indicator. That said, if you know who the right people are you usually have access to much more reliable methods.
[2] If you're still not convinced, take a politician or organization that you do like and really truly try to write an argument against that politician or organization. Note that this might actually change your opinion, so be warned.