I would say this is about status. People filter what they say to high-status individuals, but don't bother filtering what they say to low-status individuals.

Nerd culture is traditionally low-status in context of the whole society, and meritocratic inside. That means that nerds are used to hearing non-filtered things from outsiders, and don't have strong reasons to learn filtering when speaking with insiders. Also, it is more complicated for aspies to understand when and why exactly should the filters be used, so it is easier to have a norm for not having filters.

(And I suspect that people most complaining about the lack of filters would be often those who want to be treated as high-status by the nerd community, without having the necessary skills and achievements.)

Good point. It definitely does vary person-to-person, so I probably should have used individual terminology instead of "culture".

I haven't updated all the way in that direction, though. I wouldn't be surprised if certain cliques, subcultures, and cultures show significant variance in how strong each of their 4 filters are on average. I'd bet that LW is outside the mean, but we could easily be an outlier. We're too small to push the average for "nerd culture" or anything else very far, and it's certainly possible that, after correcting for confounders, it would turn out not to be a cultural thing at all.