Tragedies happen, but why can't we live with them and try solve the causes instead of results? How many people read the manifesto written by the killer? I don't agree with any brutality but there are some points to think about.
If they ban one service, they will use another one next time. Or people will watch it from an archive. Or they won't watch the it at all and trust news blindly.
But the censorship will harm everyone. It will force people to post positive, optimistic posts only. It will control what is good and what is bad. It will present a fake ideal reality.
I fundamentally support free speech and acknowledge that protecting free speech includes protecting so-called 'hate speech'. I haven't read the Christchurch shooter's manifesto but as a manifesto I would definitely include it under free speech.
However I wouldn't include live footage of violent criminal acts as free speech. Free speech is expression in words and ideas not acts. So yes, I would draw the line here and I think it is a well-defined line. (As a sidenote, a re-enactment of the crime using actors and where no-one actually dies would be free speech).
I wouldn't necessarily single out Facebook as the privacy commissioner has done but I would agree that everyone who knowingly transmits and shares this video is doing a bad thing. Again, it's not free speech it's the sharing of a mass snuff film. Which is sick.