I blame Obama-mania myself. It killed what was left of any competing ideologies (libertarians, conservative Democrats, etc.) and then LF broke off from them when Obama took private campaign contributions.
edit: To expand on this, now that I have access to a keyboard...
SA has always leaned left somewhat on culture war issues. Even in the early days you weren't going to exactly find many people arguing for church in schools, a ban on swearing or any of the American right's authoritarian ideas. But you would see some posters arguing for right wing economic ideas or for general non-intervention from the government even in areas where doing so would benefit the left or for military action abroad (that last one ended across the site as Iraq went on.)
In time most issues got a forums consensus, and anyone who disagreed would give up and not reply to the thread to avoid being dog-piled. This consensus was, with a select few exceptions, pretty much always somewhere between those of the Democratic party and the European left. 2007/8 was, in addition to the start of Obama-mania, also the peak of the Ron Paul era on the forums- buoyed by his opposition to Iraq and US foreign policy generally and his purported strict adherence to the constitution. The Paul and Austrian Economics threads were huge and fast moving. So at that point most positions in the American center were gone- you were almost certain to be a hard core libertarian or a European style Social Democrat. So about those Paul threads... they were hated by the lefties on the site's staff. And since the staff was disproportionately left leaning that meant they got to do things they shouldn't have been.
Eventually the D&D mods, who included gay, Dutch, Communist, luster-for-children McCaine and admins (such as the aforementioned Zack, Fistgrrl and Ozma) let it be known that it was open season on the libertarians. You could go into their thread and shit on it and nobody would do anything to you, assuming that thread wasn't already moved to FYAD or LF. Or you can change their avatars for money, but if they do it back to you an admin will change it to an Obama one for free.
So there you have it, you couldn't be a traditional moralistic Christian poster who believed in right-wing economics. Because you know, that type of person was a very early target of SA both on the forums and the front page. But then you couldn't be a libertarian (aka left-wing social values and right wing economics) either. So you basically weren't allowed to be any type of right-winger economically. Interestingly, you could be on the upper left side of that stupid chart- at least until McCaine got banned and then you could again when LF really went off the rails, but few people ever were and when they were it was without the religious aspect. Of course, thats just an ideology that doesn't seem to apply to many people in the developed west and as such didn't have much push outside of the "learn about the CCP" thread.
At that point LF and D&D (which was sort of falling apart-few threads were being posted in) was an echo chamber of low effort posting, anchored by a few try-hards who would basically be lolcows if the shit they were writing wasn't so infuriating. Obama was in office by this time and bound by the restraints of governance- LF quickly left him behind in their race leftward. A few of the posters, co-ordinating both on-site and off, decided to indoctrinate GBS. And GBS, being full of retards who can't debate, was totally unprepared to argue against a dog-pile of low effort leftists who would never be banned. So at that point yeah, GBS became a left-wing hivemind too. And since, contrary to what other subforums like to claim, GBS is the second biggest part of the site it naturally just spread from there. It went everywhere but Games, which moved so fast that political talk would be drowned out by talk about games. Games in Games, what a novel concept.
And of course if you went into the "no rules" subforum and posted things they disagreed with, you could end up being fucked with by the admins, banned for pretty much anything or have a Helldump thread opened on you (and then, again, banned from there.) Or they might just do all of those things even if you didn't go into their special place. And why are you complaining, you garbage person? You racist bastard. Look at this post where you said that some people abuse welfare. Etc.
And where was Lowtax during all of this? No-where. At all. He was marrying his first and second wives, buying and reselling his two McMansions, writing front page articles, trusting that radium was radically overhauling the code, experiencing the homeopathic properties of mangosteen and basically just being everywhere that wasn't the place that made him money.
Now contrary to what most people will say, that visit from the FBI wasn't the first he became aware of LF's issues. He had noticed that it, YCS and the other FYAD-lites were being obnoxious to the regular users. But he was a coward and his admins kept insisting that things were fine, so he'd do things like order the quiet deletion of invasion threads (after the off-site community that continued to plan them was already up and running) or closing Helldump, or instituting forums cancer in lieu of actually banning problem users. The only problem is, unless you're on the site all the time you wouldn't actually notice all that stuff building up. You wouldn't get the idea that SA had its own little version Halal/Haram. When it finally came time to delete LF, it took the userbase as a surprise- all the unofficial warnings to shape up were useless and Lowtax would have been better off just deleting it years beforehand. And of course by the time he did do it the other groups had left the site and they pretty much never returned.
I eagerly await the autism and powerlevel ratings.