Political free speech is essential but crass and extreme propaganda undermines proper debate, warns a Charles Sturt University (CSU) academic.

Associate Professor in political science in the CSU School of Humanities and Social Sciences, Dominic O'Sullivan, said that while by-election campaign posters displayed in the NSW city of Orange for a by-election on Saturday 12 November are legitimate expressions of free speech, they are extremely distasteful, cheapen democracy, and are unlikely to influence voting decisions.

"Clearly, these posters likening the NSW Premier and the leader of the NSW National Party to the dictators Adolf Hitler and Kim Jong-un reflect the depth of feeling against the government's reversed ban on greyhound racing and other issues," Professor O'Sullivan said.

The by-election in the state seat of Orange is to replace the Nationals' Andrew Gee who has been elected Federal Member for Calare.

"Traditional National voters may well feel that their party let them down in proposing the greyhound ban," Professor O'Sullivan said. "They may also wish to protest that the policy was adopted hurriedly and without public or party consultation, but this is not 'dictatorial' as the posters suggest.

"The decision was taken by a properly elected Parliament, and voters can change that Parliament if they wish.

"The comparison with Hitler, who killed 6 million Jews, and Kim Jung-un, who executed his uncle by feeding him to starving dogs, is a crass overstatement that will revolt many voters," Professor O'Sullivan said.

"Elections can be times of high emotion, and public policies that matter to people in deeply personal ways are raised. A by-election that will not change the government gives people the opportunity to cast a protest vote on a single issue, and many people will do that.

"Free speech is important, but so is reasoned argument.

"It is also democratically important that the people who commissioned these posters identify themselves on the posters, as is required by Division 17 (Bribery, treating, intimidation etc) (151E) of the Parliamentary Electorates and Elections Act 1912 No 41.

"The proper evaluation of a political position requires that one knows who is making it," Professor O'Sullivan said.