Liberalism:
A political or social philosophy advocating the freedom of the individual, parliamentary systems of government, nonviolent modification of political, social, or economic institutions to assure unrestricted development in all spheres of human endeavor, and governmental guarantees of individual rights and civil liberties.
http://dictionary.reference.com/browse/liberalism
Non-violent modification of political, social, or economic institutions is in the very definition of liberalism. That means that liberals cannot be terrorists.