WASHINGTON — For every black man in America, from the millionaire in the corner office to the mechanic in the local garage, the Trayvon Martin tragedy is personal. It could have been me or one of my sons. It could have been any of us.

How many George Zimmermans are out there cruising the streets? How many guys with chips on their shoulders and itchy fingers on the triggers of loaded handguns? How many self-imagined guardians of the peace who say the words “black male” with a sneer?

We don’t yet know every detail of the incident between Martin and Zimmerman in Sanford, Fla., that ended with an unarmed 17-year-old high-school student being shot dead. But we know enough to conclude that this is an old, familiar story.

We know from tapes of Zimmerman’s 911 call that he initiated the encounter, having decided that Martin’s presence in the neighborhood was suspicious. We know that when Zimmerman told the 911 operator that he was following Martin, the operator responded, “OK, we don’t need you to do that.” We know that Zimmerman kept following Martin anyway.

“This guy looks like he is up to no good,” Zimmerman said on the 911 tape.

Please tell me, what would be the innocent way to walk down the street with an iced tea and some Skittles? Hint: For black men, that’s a trick question.

Some commentators have sought to liken Martin’s killing to the 1955 murder of Emmett Till, an unspeakable crime that helped galvanize the civil rights movement. To make a facile comparison is a disservice to history — and to the memory of both young men. It is ridiculous to imply that nothing has changed.

When Till was killed in Mississippi at 14 — accused of flirting with a white woman — this was a different country. State-sanctioned terrorism and assassination were official policy throughout the South. Today, the laws and institutions that enforced Jim Crow repression have long since been dismantled. Mississippi, of all places, has more black elected officials than any other state. An African-American family lives in the White House.

Black America was never a monolith but over the past five decades it has become much more diverse — economically, socially, culturally. If you stood on a street corner and chose five black men at random, you might meet a doctor who lives in the high-priced suburbs, an immigrant from Ethiopia who drives a cab, a young aspiring filmmaker with flowing dreadlocks, an unemployed dropout trying to hustle his next meal, and a midlevel government worker struggling to put his kids through college.

Those men would have nothing in common, really, except one thing: For each of them, walking down the wrong street at the wrong time could be a fatal mistake.

I hear from people who contend that racism no longer exists in this country. I tell them I wish they were right.

Does it matter than Zimmerman is himself a member of a minority group — he is Hispanic — or that his family says he has black friends? Not in the least. The issue isn’t Zimmerman’s race or ethnicity; it’s the hair-trigger assumption he made that “black male” equals “up to no good.”

This is one thing that hasn’t changed in all the eventful years since Emmett Till’s mutilated body was laid to rest. It is instructive to note that Till grew up in Chicago and just happened to be in Mississippi visiting relatives. Young black men who were born and raised in the South knew where the red lines were drawn, understood the unwritten code of behavior that made the difference between survival and mortal danger. Till didn’t.

Today, young black men grow up in a society where racism is no longer deemed acceptable. Many live in integrated neighborhoods, attend integrated schools, have interracial relationships. They wonder why their parents prattle on so tediously about race, warning about this or that or the other, when their own youthful experience tells them that race doesn’t matter.

What could happen on the way home from the store with some Skittles and an iced tea?

Whether Zimmerman can or should be prosecuted, given Florida’s “stand your ground” law providing broad latitude to claim self-defense, is an important question. But the tragic and essential thing, for me, is the bull’s-eye that black men wear throughout their lives — and the vital imperative to never, ever, be caught on the wrong street at the wrong time.

Eugene Robinson’s email address is eugenerobinson(at)washpost.com. (c) 2012, Washington Post Writers Group