If you post a photo of a rifle on Instagram, tag it to your hometown, and add a caption like “green tip armor piercing gets the girls wet," Maryland police can cite that to get a no-knock search warrant and kill you in a pre-dawn assault on your bedroom. In his novel Nineteen Eighty-Four, George Orwell warned, “If you want a picture of the future, imagine a boot stamping on a human face— forever.” Duncan Lemp, the 21-year-old software programmer who posted the rifle photo I've just described, was shot three times without warning by a policeman standing outside a smashed-in window at 4:42 am....