So, the legal system in most countries is that if you post something explicitly (not in jest, or metaphor, but quite deliberately and with the intent of other people's death) asking people to murder other people, that is something that you perhaps ought to be charged with an offence over.
Meanwhile Facebook, etc, essentially argue that ok, they posted a request for the murder of a lot of people, but hey, we took it down after only a few thousand people read it, and we've closed the account (until they open another one), so that's job done, no need to prosecute any further, you shouldn't ask us to cooperate with police, we've got adverts to sell here.
Small wonder that governments are changing the law, when tech companies regard requests to kill people as something that, if really pushed, they'll treat as equivalent to how they handle copyright infringement, but actually there's less money in it for them so would you mind if it was a bit further down the planned feature list.