I am Trayvon Martin.

So are you. And so is any human being who has ever felt cornered, in a dark and desolate alley, between life and death. Add the grim reality of skin color in America, and you have the disastrous spectacle of 250lb George Zimmerman, 28, pursuing 140lb Trayvon, 17, until that man-child is screaming "Help!" – and then gasping for air after a bullet from Zimmerman's 9mm handgun had punctured his chest. A majority-white, gated community became, on 26 February, the makeshift mortuary for a black boy who will not get a chance to live, to go to college with his exceptional high school grades, to make something of his life. Trayvon's fatal act: a mundane walk to the nearby convenience store to buy a can of iced tea and a bag of Skittles.

This is what racism, the American version of it, means to black boys like Trayvon, to black men like me. That we often don't stand a chance when it has been determined, oftentimes by a single individual acting as judge and jury, that we are criminals to be pursued, confronted, tackled, and, yes, subdued. To be shocked and awed into submission.

The police authorities in Sanford, Florida, where the shooting occurred, are apparently so mired in racial prejudice and denial that George Zimmerman, at this writing, still has not been arrested nearly a month after Trayvon was killed – in spite of Zimmerman being told, on 911 police dispatch audio, not to follow Trayvon Martin.

In spite of Zimmerman being charged in 2005 with resisting arrest with violence and battery on a police officer. In spite of Zimmerman calling the police 46 times since January 2011. In spite of Zimmerman, according to neighbors, being fixated on bracketing young black males with criminality. In spite of Zimmerman being the subject of complaints from neighbors in his gated community due to his aggressive tactics. In spite of the officer in charge of the crime scene also receiving criticism in 2010 when he initially failed to arrest a lieutenant's son who was videotaped attacking a homeless black man. In spite of Zimmerman violating major principles of the Neighborhood Watch manual (the manual states: "It should be emphasized to members that they do not possess police powers. And they shall not carry weapons or pursue vehicles.")

In spite of Zimmerman not being a member of a registered group, which police were not aware of at the time of the incident. And in spite of the Sanford, Florida police failing to test Zimmerman for drugs or alcohol. (A law enforcement expert told ABC that Zimmerman sounds intoxicated on the 911 tapes, and that drug and alcohol testing is "standard procedure in most homicide investigations".)

Finally, what was a man like George Zimmerman doing with a gun in the first place? And will Florida's very controversial "stand your ground" self-defense law prevent Zimmerman from ever being prosecuted, especially as he and his lawyers are claiming he was protecting himself from harm?

Finally, does any of the above truly matter, if the shooter has white skin and the victim's is brown?

We've heard, since President Obama came into office, that we suddenly, miraculously, live in a "post-racial" America, that there now is such a thing as "post-blackness". Try telling that to the families of Trayvon Martin. Or Ramarley Graham. Or Sean Bell. Or Oscar Grant. Or Amadou Diallo. Or Emmett Till. Or the Scottsboro Boys. And numberless others in modern US history.

Racism remains the greatest cancer of American society, and has been since the founding of this nation – by men who owned slaves. You cannot slaughter and push from the land Native Americans, enslave black people, harass and marginalize Asians, Latinos and Jews, and scapegoat immigrant white ethnics and Arabs through your long and tumultuous history, then wonder how the killing of Trayvon Martin could happen in the first place? The former is the context for the latter.

We, most of us, have been socialized to fear and demonize difference, the other. Trayvon's murder is of a piece with hysterical and overzealous anti-immigration policies and new voter ID laws that recall the days of segregation and harsh American racial apartheid. Left unchecked, as George Zimmerman has been left unchecked, and you perpetuate this ugly national tragedy.

American racism is not merely a distortion of human psychology that teaches the George Zimmermans of our nation to see Trayvon Martin as nothing more than a criminal; it is also the debilitating disease that allows us, on the one hand, to denounce the alleged atrocities of Kony in faraway Africa we've seen in that ubiquitous viral video, and on the other, to overlook the Trayvon Martins, just as we ignore the routine stop-and-frisk harassment of legions of black and Latino young males.

We are trapped in the stereotyping that saw my friend's son being told by his teacher in Fairfax County, Virginia recently, as he reciited a Langston Hughes poem, that he needed to read it "blacker". The stereotyping that allows us to cheer loudly for the majority-black college basketball teams during March Madness, yet won't permit us to pay attention to Trayvon Martin's parents, clearly shattered, pleading for some shred of justice.

The Justice Department's intervention is welcome, if belated. But it is American racism that constrains our leaders, like President Barack Obama and Attorney General Eric Holder, from speaking forcibly and publicly about this destructive cancer for fear of alienating "regular" folks. If the president could call on Sandra Fluke considering the insult she'd received from Rush Limbaugh, we should be able to expect him to offer his condolences to Martin's parents for the grevious injury they have received.

For the sake of Trayvon Martin, and the Trayvon Martins who never had this sort of mass outcry, something must be done. But if we choose to turn our ears and hearts away from his parents and his community, then Trayvon Martin's blood will be on the hands of this entire nation. Will we ignore that call for help, as Trayvon's went unheeded?