What did Lucanus mean by "The sin of thousands always goes unpunished" in Book V of Pharsalia?
That the sins committed by the mass public are unpunished and ignored. Sometimes people don't even recognize the actions as crimes but as social norms (ie downloading music off the internet). Also, sometimes the crime is so unusual there is not even a law for it, so then it becomes a question of moral punishment. Basically, if enough people do it, no one gets punished because of the size of the population committing it.