The Muslim activist who sparked an uproar with a planned lecture on honour killings won't say if he believes they are justifiable, telling critics they will have to wait to read his writing on the topic instead.

Hizb ut-Tahrir spokesman Uthman Badar says the backlash against his slated Festival of Dangerous Ideas talk says more about bigotry in Australia than it does about him.

The Sydney Opera House cancelled Mr Badar's lecture "Honour killings are morally justified" within hours of announcing it on Tuesday.

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