I'm not an expert in KiwiFarms, but I think the difference between the goverment putting you to death and what KiwiFarms does is they don't put you to death. My understanding is they basically talk shit about people and talk to each other about how to let the person they dislike know how much they dislike them. It's a nasty and horrible version of protesting.
Say you dislike Donald Trump and you want to talk shit about Donald Trump and you want to organise a protest againist Donald Trump, you want to hurt his interests by organising a boycott of his companies, or say random things like you wish he was blown up, etc. This would be roughly the same as what I understand KiwiFarms do. Big difference is, KiwiFarms do this to random people for no other reason that for laughs from people they call lolcows.
These are trolls. Nasty horrible people. However, my understanding is they don't put people to death or even commit acts of violence. They are the internet version of the Phelps family.