Leftbook is a group of
Facebook groups that are run by very left-wing admins and moderators. They are not united under one group of leaders, but rather under a general very left-wing ideology. They are especially known for advancing modern "social justice" causes and frequently banning users. This tends to create a toxic environment where people are constantly worried about being banned for expressing any view that offends anybody. The groups frequently require users to oppose capitalism, support
modern feminism, defer to the opinion of any member of a minority group (even if other members of that group do not always agree), constantly apologize for their own privilege if they are white/male/straight, support Antifa, unquestioningly support the opinions of mods, etc. This basically shuts down any dissent because those people either get banned or are afraid to speak up. In order to avoid being banned, many members dogpile anyone else who comes under criticism as a way to virtue signal and build their own reputation.
These groups have come under fire from other leftists for being hostile, unintentionally being ableist because many autistic people struggle to navigate their byzantine social norms and get banned without being given an explanation for what "mistake" they made, being
counter productive by pushing people away from the left, and of course for being
authoritarian.