Hypothesis: People who IRL are relatively well-connected socially (but feel obliged to conceal many of their views from their meatspace associates) and people who actually feel socially isolated or alienated IRL will have divergent views about the optimal level of familiarity in this online community.

Probably true, but if one suffers from social isolation and alienation in meatspace, trying to remedy that situation by seeking internet friends in a place like this one would likely be a highly suboptimal (to put it charitably) way of addressing that problem.

For what its worth, I think abrasiveness breeds more contempt than does familiarity.

It might conceivably breed more ill feelings in general, but not contempt in particular.

I agree that abrasiveness is better avoided too, though.

Agreed, though I also think "abrasive" and "familiar" are terms that only make sense relative to some specific notion of what the unmarked baseline is. Personally I find very most of the discussion on LW neither of these things.