I'm feeling slightly paralyzed by the realization of how old I've become in relation to the online history of this scene... but putting that aside for a second, I think I can explain the answer.
Pull up a chair, young ones (or at least those new to this), and I shall tell you of days of yore. Let me tell you of the days of high adventure! (and by "high adventure", I mean people typing things at keyboards...
woo!)
[for the sake of sanity, this isn't going to be as long as it could be --however it should trace the lineage of this forum and explain how we got here]
In the before time, there was the DHP Mailing List. Neo fans across the world shared ideas and had fun. Later came the websites. One of several notable websites in the mid-1990s was Neo-Alec's, at the time run by a student (he's actually a member here now). Another website was DolphinLord's. Both had forums, though neither particularly supplanted the mailing lists. However a number of the oldest members here found the online community through these various channels. This was the time of more innocent collecting and far less talk of scams and other BS.
Around 1998/99, the infamous duo of Dion Dakis and Chris Ray appeared on the Neo scene. Dakis had previously appeared on the DHP, asking fairly innocuous questions about the Neo Geo --stuff that anyone getting into the hobby would. Chris Ray has a technical background and is competent with engineering. Both were enthusiastic collectors. However, at one point they decided to start a business that claimed that their conversions were better than the originals, and their inserts (while color coordinated and much more universal than those officially put out by SNK and its licensees) should be used instead of any official inserts. They began claiming that certain games that were only available on MVS were available on NGH/home/AES (the latter was an acronym that they popularized). For a while people believed, and they certainly didn't claim otherwise, that the carts they made were the real, official deal. They started their own mailing list, but things soon went south as individuals picked up on their antics/propaganda and started "disappearing" from their mailing list. They later shifted to the growing platform of Yahoo Clubs (this is still the late 90s), where the founded Neo Geo Heaven. The duo, who soon formed Neo Geo Freak (NGF) for their work, played an effective hand of promotion through claimed exclusivity and exorbitant prices. They claimed that people who purchased their set of high priced conversions (sold as "official NGF") would be "Big Tymers". A lot of people saw them as con men. They did a great job of penetrating the community, and here we see the beginning of the current attitude you mention.
As a response another Yahoo club, DolphinLord's Neo Geo Domain, was founded and became a center of sorts --and the basis for a number of people who ended up here. There was definite sniping between NGF and DolphinLord's, but ultimately the Yahoo Club format was very cumbersome (it only had one, big thread). You should realize that, by this point, the Neo Community --at least this corner-- became about revealing the truths, half-truths and lies that had pervaded and spread.
In August 2000, Shawn, a fairly recent collector and member of the Yahoo Club, decided to launch Neo-Geo.com. Shawn's forum was well built and soon the membership of the Yahoo Club seeded the bulk of this website's original members (DolphinLord became a moderator here). The original membership was pro-collector and virulently anti-ROM-piracy. The extremely valuable domain name quickly drew in more people with interests in the Neo-Geo. In early 2001, not long after the site's formation, another forum named Orochinagi.com was suddenly merged with NG.com after its server shut down --this was brief, dramatically ugly, and unsuccessful (too many differences on key things like ROM piracy) --this kicked up tension, but not as much as NGF:
From the beginning, Shawn wanted this website to be an open forum for ideas and discussion --and important factor to a lot of people who were burned by NGF's claims and lies. Needless to say, when NGF started promoting their wares here, it didn't go nearly as well as it would with a controlled audience. Flames followed. The culmination was the infamous KOF 2000 US edition: After the closure of SNK USA, NGF managed to convince SNK Japan to let them release the game in the English markets, however they made alterations that stamped their URL in certain corners of the insert. After lots and lots of drama, that relationship soon ended, and Shawn's NeoStore became the official release partner for English releases (though he too was subject to intense scrutiny from some members of this forum --after all, who could tell who was being honest?). The end of NGF as a major player was when SNK sued them, had their offices raided, and the practice of NGF "corrected" carts and inserts pretty much faded away by 2003. Some members remained longtime advocates of NGF until the bitter end --though most eventually came around (and often became the most hostile towards those two).
In addition, as was correctly pointed out, the existence of ridiculously high priced games and a market for them led to a number of cheats, scammers and other ne'er-do-wells. There are many more stories, but those were the ones that crafted the attitude of the forum, and explains why it must seem strange for anyone walking in now in 2009... heh.
Want to know more? --there's stuff in this Glossary:
http://www.neo-geo.com/reviews/NeoGlossary/neoglossary.htm
