Why do you think such an approach would work, but something equivalent to try to prevent mass shootings / school shooter type gun violence wouldn't? Or would you say that radical open cooperation and mutual self restraint led by governments could stop the American problem of mass shootings like the Las Vegas shooter?

I don't see how you stop terrorism (of the school shooter type, not the Islamic/political type) with inter-government cooperation. Mirror life is just another vector for school shooters but with PHDs.