What is now referred to as the AnCap exodus was an event in July of 2011 where several members left the site in protest of certain actions by the moderators. Most of the members who left identified as anarcho-capitalists, hence the name.
Before the events that directly caused the exodus, there was a lack of moderation on the site. Therefore one member, askbob, took it upon himself to get rid of trolls and other members he found detrimental to the site. The preferred method was to out their personal information. Many of the people askbob attacked were admittedly trolls or extremely detrimental members of the site, however there were instances where he went after normal members such as Insertnamehere, Cerebral_Narcissist, and Darkkermit. This made him a polarizing figure, with some defending him and others condemning.
Brainmaster was a young DDO member who attracted the attention of askbob by some of his trollish actions. Askbob outed Brainmaster's personal information, even going so far as to make a personal photo of him his profile picture. The moderaters stepped in and banned askbob for this (having dealt with similar instances of a similar nature with him), claiming legal liability as their motive. Many of askbob's supporters took this to be the last straw in what they considered to be the collapse of the site intellectually and admin-wise and left.
Those who left
Those who left may be divided into two groups, those who left and never came back and those who left but later returned. Belonging in the former group were members like askbob and Sieben (who were both banned) as well as members like J.kenyon, and Freeman. Those who left but later returned include Cody_Franklin, Reasoning (for a short time), Socialpinko, and Tvellalott.