Anti-system parties may pose an acute dilemma for democracies: Banning a party may help to defend democracies from extremists managing to obtain representation in parliament, but proscription risks undermining foundational liberal democratic commitments to free association, free speech and the representation of all citizens in the public sphere. However, democratic states respond to the dilemma in different ways. A cursory examination of the lists of parties banned in the post-world war two period (Bourne, 2012 and Bourne and Casals, 2014) shows that many parties of similar types (eg. communist, far right, secessionist, political wing of terrorist groups) have been banned in some democracies but not others. This variation in responses to anti-system parties raises the principal puzzle I explore in the paper: Why do some democracies respond to the dilemma posed by anti-system parties by banning them, while other democracies do not?
