An early slide in the talk did warn that it would contain content that was not suitable for under-12s.
On one hand, this is good and I could have chosen to walk out if I had wanted to - though there was no sub-text like the OFLC provides: e.g. "profane language, sexual imagery". "simulated violence" etc. That would have informed my choice more effectively. I don't think censorship is appropriate (for adults), but I do believe in "informing your choices". Mark made a step in that direction which should be commended, but it wasn't a very big step.
On the other hand, the fact that he clearly knew it was offensive in this way and went ahead with the talk was, I think, misguided. Certainly I think it is appropriate to shock your audience some times, but in this case I think the bare facts, when explained as Mark explained them, are shocking enough. If provocative imagery is wanted, I feel that imagery of slavery would be much more apt and less contentious than the imagery that was used.
(OFLC == Office of Film and Literature Classification in .AU)