SYDNEY—CNN said it is preventing Australians from accessing its Facebook pages after a court ruled that publishers can be liable for defamation in public comment sections and the social media firm refused to help it disable comments in the country. The move makes CNN, which is owned by AT&T Inc., the first major news organization to pull its Facebook presence in Australia since the country’s highest court ruled this month that publishers were legally responsible for comments posted below articles—even if the articles themselves were not defamatory. The ruling has come under much fire with defamation lawyers accusing Australia of not keeping up with technological change and noting the contrast with the United States and Britain where laws largely protect publishers from any fallout from comments posted online. Australia is currently reviewing its defamation laws but in the meantime, other global news organizations, especially those that feel they can easily …