Los Angeles debates the treatment of illegal immigrants. Sometimes a solitary tragedy can weave all the tangled threads of a far-ranging debate into a sharply focused picture, one that only the willfully blind can claim not to see. Here in Los Angeles, one such tragedy has been the murder of Jamiel Shaw, 17, a high-school student and star athlete who was shot to death on March 2 of this year. Pedro Espinoza, a 19-year-old gang member, has been charged with Shaw’s murder. More than 100 people have been murdered in Los Angeles so far this year, and if this was...