Since 2002, the New York Police Department has taken tens of thousands of weapons off the street through proactive policing strategies. The effect this has had on the murder rate is staggering. In the 11 years before Mayor Michael Bloomberg took office, there were 13,212 murders in New York City. During the 11 years of his administration, there have been 5,849. That's 7,383 lives saved—and if history is a guide, they are largely the lives of young men of color.

So far this year, murders are down 29% from the 50-year low achieved...