> the only reason family ends up ratting these people out is because of the high pressure it ends up on the family.

That is not true. There was no pressure on unabomber brother - he "ratted" him out entirely on own will. Also Elliot Rodgers parents called police after they read the manifesto - before any pressure happened. Ex wife of DC shootings had restraining order on him, feared him, and when police asked whether she thinks he is capable of violence like that her first answer was "yes".

The thing also is, these people are often assholes in their own lives, toward relatives too. They tend to have track record of domestic violence and abuse.