2011’s The Purge, written and directed by relatively green film-maker James DeMonaco, was a concept in search of a movie. The ropey home invasion flick was built around an irresistibly trashy hook: in less than a decade from now, America is a sort of Tea Party NRA wonderland where, for one night a year, violent crime is legal. Murder is not just allowed, but promoted as a civil duty, all the name of spiritual self-renewal. It keeps the crime and population numbers down and the welfare rolls under control (dead people don’t claim the dole). The low-budget but decent-grossing film…