Geek Social Fallacy #1: Ostracizers Are Evil
GSF1 is one of the most common fallacies, and one of the most deeply held. Many geeks have had horrible, humiliating, and formative experiences with ostracism, and the notion of being on the other side of the transaction is repugnant to them.
In its non-pathological form, GSF1 is benign, and even commendable: it is long past time we all grew up and stopped with the junior high popularity games. However, in its pathological form, GSF1 prevents its carrier from participating in -- or tolerating -- the exclusion of anyone from anything, be it a party, a comic book store, or a web forum, and no matter how obnoxious, offensive, or aromatic the prospective excludee may be.
As a result, nearly every geek social group of significant size has at least one member that 80% of the members hate, and the remaining 20% merely tolerate. If GSF1 exists in sufficient concentration -- and it usually does -- it is impossible to expel a person who actively detracts from every social event. GSF1 protocol permits you not to invite someone you don't like to a given event, but if someone spills the beans and our hypothetical Cat Piss Man invites himself, there is no recourse. You must put up with him, or you will be an Evil Ostracizer and might as well go out for the football team.
This phenomenon has a number of unpleasant consequences. For one thing, it actively hinders the wider acceptance of geek-related activities: I don't know that RPGs and comics would be more popular if there were fewer trolls who smell of cheese hassling the new blood, but I'm sure it couldn't hurt. For another, when nothing smacking of social selectiveness can be discussed in public, people inevitably begin to organize activities in secret. These conspiracies often lead to more problems down the line, and the end result is as juvenile as anything a seventh-grader ever dreamed of.