Male human beings between the ages of 13 and 25 are dangerous. Deadly dangerous. Before that age they're too small to be much of a problem, and after that age they usually have something to lose and know not to cause trouble. But the teens-to-twenties are a hard time for all of them, and because of that it's a hard time for all of us.
A significant number of teenage men (of any race, color, creed, religion, country, or culture) are little more that very bright chimpanzees. They murder, steal, lie, cheat, and destroy things with such alarming regularity that large sections of them are simply abandoned by American society. And it's not just urban poor or minorities. The richest white boys in my school were every bit as dangerous as the poorest blacks, perhaps even more so since the white kids' parents would cause even more trouble, convinced that their little angel couldn't have been the one to, say, drive a dozen golf carts into a swimming pool or shoot their fiance with a shotgun. Once abandoned, they complete the transition to bright-chimpdom and form that time-tested bugaboo of urban society, the youth gang.
Why does this happen? In no small part because we no longer can afford wars. Cultures going back to Paleolithic days have understood that a large predator with a powerful brain and no real stake in society is an extremely dangerous thing to have wandering loose in a village. So rather than have them making trouble in the local area, elders would gather them up and point them at somebody else's village. This had many positives: it kept the boys busy, got rid of the ones that were too stupid or slow, let them vent their urges in a way that was safe to the village, and sometimes the boys would return with loot and new women.
Of course, it wasn't a perfect solution. You didn't live in a vacuum. Other villages got the same idea and sometimes their boys would come your way and wreck your place and steal your women. Sometimes the other village was a lot tougher than you expected and nobody came back. And other times one particularly bright, strong, or dangerous kid would decide he could run the place better than you and use the boys to kill you instead.
But, overall, it worked. And from the Stone Age on down this practice became the normal way to ensure teenage males didn't cause too much trouble. In the past there certainly were bumps in the road. The earliest discoverers of agriculture found that using the boys to work instead of fight brought bigger harvests and kept them nearly as busy. Unfortunately there were lots of other societies that didn't do this, and the only thing that's worse than having an army you can't control very well is having no army at all. These societies got replaced pretty quickly with ones that knew a smaller harvest you get to keep is worth not using every strong male hand for farming.
Innovations and refinements occurred throughout the agricultural era. Organization, discipline, conscription, tactics, strategy, and constant improvements in weapons turned what started out as a rabble of screeching naked chimps into what we would now recognize as a standing army.
Unfortunately for society as a whole, industrialization changed all the rules. Weaponry got really destructive, and really complicated, really fast. Attempts at forcing the old ways using the new weapons resulted in global apocalypses.
A professional army of volunteers, an idea once thought to be self-evidently absurd, has proven to be the only way to effectively manage the complexities of the modern battlefield. A sullen teenager that doesn't want to fight isn't much of a problem when someone is howling and running at him with a spear. He fights or he dies. And it doesn't take a genius to learn how to use a sword. But a sullen teenager is a problem sitting behind a computer screen miles away from a battlefield, and it does take a genius to, say, fly a modern combat aircraft and actually hit anything with it.
These new rules have only been in effect for the past century or two, so we still haven't found any really good answers. Some societies continue to conscript, but all that does is give you a huge army of infantry. Others require civil service, but working for the government doesn't control the really violent ones, and is also expensive and prone to corruption. Other societies are lucky enough, and homogenous enough, that everyone agrees ahead of time what must be done with the young men, and have the social cohesion to make it stick.
Of course, none of that does the US much good, and it shows. We were one of the first to give up on conscription, and it almost requires a PhD to run some of the weapon systems we use. It's also no coincidence that we have the most powerful, best controlled, military in the world. We also have a strong tradition of not using government jobs as a form of unemployment insurance. It's no coincidence either that we have the most powerful, most efficient economy in the world. We're so heterogeneous we have heated arguments about the color of the sky. And it's no coincidence that we are the most innovative society on the planet.
So we're kind of stuck. The methods that work for most of the rest of the world don't work for us, and for good reasons. But that leaves us with all these naked chimps running around causing trouble and breaking stuff. And because of that, we're all in danger of something as simple as walking down the street wearing, or simply being, the wrong color.