If the option was left in the preferences menu (roughly where the anti-kibitzer is kept) I expect a small minority (about one in ten posters) to actually flip the Crocker bit. I actually think the level of politeness expected towards people who do turn on Crocker's Rules will be more interesting: there is a mentality that translates "politeness required: 0" into "politeness required: arbitrarily large negative number" ("no need to be polite" -> "be extremely rude"), and I think there's a nonzero chance of that mentality being present on LW.