They aren't but they are responsible in the sense that they shouldn't give that shit a platform.
This statement could be used about literally any topic that certain groups of people find objectionable. The US is currently providing a very clear example of what happens when you use that argument.
Other people did that to him.
Seeing as he was an active participant in it, this is the core of my questioning. Why is it considered 'something others did to him', and not 'something he did to himself'? He could have left at any time, but he chose to stay and remain in the activity.
freeclimb metaphor doesn't work as well as harm is not the goal of free climbing. The goal is to reach the top. Dying is a risk you take.
Harm was not the direct goal of this stream either. The goal was to see how long they could stay awake. Heck, take boxing. Boxers still die every year, and that's a much more obvious example of harm being the direct goal of the activity. Nobody is seriously suggesting that boxing should be criminalised, or that participants should be prosecuted.
But I think this is not a this-one-person-is-responsible-situation. Everybody in the chain of events that lead to this mans death is responsible in some way. Everybody who knew and did nothing.
There is a gradient of responsibility, of course. The person just watching isn't as responsible as the person who is acting, but everybody is guilty to some degree. And to that degree people should be punished.
I agree that everybody involved is in some way indirectly responsible. However I'm unclear that it's actually illegal. Morally reprehensible, but morality is a very subjective opinion and one I'm very hesitant to let platforms start deciding on my behalf.