An ideologue is a person who is a proponent of a particular set of ideas. Such a person may be admired by many while being hated by others. The reason this happens is because in order to be an ideologue, one must support ideas that are far from center. Politically speaking, Rush Limbaugh is a right-wing ideologue while Al Sharpton is a left-wing ideologue.
Ideologues are brave people who lack common sense. Limbaugh, for example, sometimes states opinions that make no sense or he defends people that are indefensible. He also seeks to pick on people who are opposed to his viewpoints. The same can be said about Sharpton. He divides people by racial lines and will, just like Limbaugh, side with the opinion that best supports his ideology, whether the opinion is right or wrong.