A hot summer weekend, when Chicago should be at its most livable, brings an undercurrent of dread and horror to this city. Summer is block party season, beach season, baseball season. But in some neighborhoods, summer is killing season — when armed gang members run amok firing at each other and anyone in their way.The death and injury total from Friday night to Monday morning numbed the senses: At least 74 people were shot, 12 of them killed, according to a tally by Tribune reporters. Those are figures from a war zone; they shouldn’t reflect the reality of an August weekend in an American city.Chicago is the nation’s bleak outlier, where a culture of violence and bloodshed devastates some areas.Mass shootings in Chicago often involve gang members targeting rivals. Summer weather brings more people outside, which creates more opportunities for mayhem. Fred Waller, Chicago Police Department’s chief of patrol, told reporters a bad guy with a gun may be aiming at one person but will give zero thought to others in the field of fire. "You shoot aimlessly like that, you are shooting into a crowd," he said.Waller blames the violence on the proliferation of illegal guns in the city. But he also blames "the culture," because Chicago’s terrible tradition of gun violence is connected to many aspects of life in struggling pockets of the South and West sides. He said gang members engage in mindless violence without any fear of consequence: If they’ve used a gun and are not incarcerated, they’ll do it again. That’s the life they know.A lack of job opportunities contributes to hopelessness. Families are fractured, creating a shortage of positive role models. Soon, another generation coming of age is lost. "We need parents to be parents," police Superintendent Eddie Johnson said at a news conference Monday. "We need neighborhoods to be neighborhoods," he said, asking for help identifying suspects. "You all know who these individuals are, they come into your homes every day, sleep with you every night. Grandparents, parents, siblings, significant others — you know who they are."This does not absolve CPD of responsibility for apprehending violent criminals, or the courts from using toughened sentencing guidelines to get repeat offenders off the streets. The police need community members to help fight crime, but Chicago has, along with its gang problem, significant trust issues between police and residents in some neighborhoods. That’s why it’s crucial for City Hall to sign off on a consent decree to start court monitoring of policing reforms.The violence goes on and on, from killing season to killing season. It is the city’s great shame and cannot be forgotten.