Censorship has become the talking point at Bali's famous writers festival, which got under way with police in the background.
The Ubud Writers and Readers Festival, founded by Australian Janet de Neefe 12 years ago, was pressured to scrap sessions from its program for the first time this year.
Discussions, an art exhibition and film screening on the 1965 communist purge were first cancelled, and other events followed, including one about the contentious development of Benoa Bay.
Police were present outside festival venues on Thursday, with one officer seen taking photos after the opening, but from a distance.
Censorship has become one of the festival's talking points, with Jakarta Post senior editor Endy Bayuni devoting his keynote address to the topic.
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"History shows ... that once they get away with banning one event, let's say a public discussion on a particular issue, they will ban the next one," he said.
"Once we allow or tolerate censorship, we will never see the end of it."
Melbourne academic Katharine McGregor, co-coordinator of the programs cancelled, says the authorities' actions have also put the spotlight on the subject they were trying to suppress.
"I've been really surprised at how many people, Indonesians as well, have come out in the press condemning this," she said.
"Not just for freedom of speech, but saying also it's time to have an open discussion about 1965. That's very reassuring."
The massacre of more than 500,000 people is one of the largest mass murders of modern times.
President Joko Widodo rejected the idea of an apology to victims' families on the 50th anniversary.
Local police chief Farman told AAP this week: "In Indonesia, there are sensitive things, there are things that should not be discussed."
