The reasons above are all true, but the "creative moderation" that twisted legitimate debate and discussion about the bifurcating future of Bitcoin as either a person-2-person or settlement network into altcoin censorship gave this forum a final huge kick in the nuts.  It was a huge loss-of-confidence in the impartiality of this forum regardless of which side you were on.

And whether you agreed or disagreed with the author of the GCBU thread about that issue, the fact remains that he provided an awesome distillation of and commentary on current world economic events.  GCBU readers would then pop off and comment on other threads in speculation. 

Basically this forum and bitcoin discussion as a whole just had its Mt. Gox moment.