Misguided fools that don't understand what the American Civil Liberties Union is all about. The aclu defends people and organizations that face threats to their Constitutional Rights. The Constitution is meant to protect Americans from the powerful government, corporations and/or individuals. Remember everyone is created equal? The aclu takes on cases to defend people's civil rights, particularly those in the 1st Ammendment: freedom of the press, religion, speech and assembly.
ACLU bashers are usually just misinformed fuckwits, however some neocons actually are opposed to the idea of a group defending the rights of the little guy.