That's not even an argument. So people should be allowed to watch child porn?

Plenty of parallels between the two. People are hurt in the filming of both. It's damaging to the survivors. It feeds into the fetishes of those who would watch such a thing (it's a snuff film). In the case of this film I could argue that potential perpetrators could study the film for their own plans.

In a forum discussion on the shooting, I found a link. I clicked the link, realized it's the right video from descriptions and asked myself 'WTF am I doing? If I keep watching, that's going to have consequences for life and stopped.'.