The most talked-about local story of last week was a Saturday-night ambush of a BART train by 40 to 60 youths at the Coliseum Station. It was unquestionably a scary scenario for anyone who rides BART: The youths hurdled over the fare gates, held open the doors of the Dublin-bound train, and seized cell phones and bags from seven passengers. Two passengers suffered face and head injuries.

Within moments of the first version going online, the reaction came fast and furious on SFGate. The story had more than 2,100 comments by week’s end. And a considerable portion of the anger was aimed at what was not in the story: the race or races of the young mob, which BART did not reveal.

But that did not stop readers from jumping to conclusions.

“‘The images can’t be shared publicly’ ... translation: black kids,” said one post.

The exchanges only got uglier, as stereotypes and racial resentments flowed out of the closet.

“More of Obama’s kids acting badly.”

“If one of these kids would have been killed by a cop, Oakland would be in flames right now.”

“No crime here ... they were merely taxing people for white privilege.”

Some commenters suggested passengers should start packing concealed weapons. A few even invoked the name of Bernhard Goetz, the infamous “subway vigilante” who in 1984 shot and seriously wounded four African American teens after one of them demanded $5 and Goetz was convinced he was about to get mugged.

A “Bay Area Bernie Goetz needs to Oscar Grant each and every one of those cockroaches,” said one post, alluding to the Jan. 1, 2009, fatal shooting of Grant, an unarmed and restrained 22-year-old black man, by a BART police officer at the Fruitvale Station.

“Black males are the most violent group in America,” wrote another.

But here is the reality: The youths were not all black — and not all male. Some appeared to be as young as middle-school age. And not every one who jumped the fare gates was directly involved in the robbery.

“I saw the video,” said BART spokeswoman Alicia Trost, who described it as “super crystal-clear” high definition. “There was some diversity in there.”

BART has refused to release surveillance video, citing what I would regard as an overly narrow interpretation of state law about evidence of crimes involving a minor.

If the videos had been released, it would have no doubt led to a discussion in our and other newsrooms about which parts were relevant to post. Among the issues: How graphic were the images of violence? What would be the enduring impact on both the victims and the very young people in the crowd who may have been swept up in the moment but did not block doors or rob anyone? Would the video be of value in identifying those who deserved to be charged?

As it was, the video has allowed BART to identify perpetrators, Trost said. The first arrest was made Friday.

The video controversy aside, the coverage and reaction to it does raise questions of journalism ethics: Was the race of the youth relevant to the story? Should a news website facilitate such overtly racist vitriol under a cloak of anonymity?

As overseer of the opinion pages, I am not involved in the decisions on news coverage or online comments, so I went to those who make the judgments for answers.

Trapper Byrne, The Chronicle’s metro editor, explained, “We’ve long had a very specific standard for including a suspect’s race or ethnicity — it has to be part of a complete description that includes such details as approximate age, build and distinctive clothing.” In this case, he added, “We had no such detailed descriptions.”

He makes a very fair point. To avoid a gratuitous and hopelessly broad description of a suspect (what value is it to know the suspect was “a black man between the ages of 35 and 50 and between 5 feet 9 and 6 feet tall”?) is not a matter of being politically correct. It’s about pertinence and precision.

On the matter of the racially charged comments, SFGate Executive Producer Brandon Mercer explained that the site has a historic commitment as the “modern-day equivalent of a town square.” While owned by the same parent company, the Hearst Corp., SFGate and The Chronicle (and its subscription website, SFChronicle.com) make their independent judgments on editorial content — including comments, of which SFGate creates far wider boundaries on discourse that might be considered offensive to some.

“Just like publishers have a constitutional right to free speech, I believe the public deserves a place to have their say on the news, and commenting allows that,” Mercer said.

A couple of footnotes to this story:

SFGate has a national, even global, audience, so the racist vitriol did not necessarily emanate from the Bay Area. The right-wing Drudge Report linked the SFGate article about the BART ambush on its website and Facebook page, and the comments there were similarly drenched in stereotypes about race, Oakland and liberals.

It’s also worth noting that the story drew submissions to our letters to the editor, which require a reader to provide a real name, city and a phone number for verification. Readers were rightfully concerned about what the story revealed about BART’s security vulnerabilities and the state of our society. Can you guess how many of those readers who put their names to their public statements ranted about race?

Zero.

John Diaz is The San Francisco Chronicle’s editorial page editor. Email: jdiaz@sfchronicle.com Twitter: @JohnDiazChron

Did BART intentionally downplay the April 22 train ambush?

Several commenters on SFGate demanded to know why a robbery that occurred at 9:35 p.m. on a Saturday night did not get reported in the media until Monday. “How is it possible that this did not make Saturday or Sundays news?” asked one reader. Here’s how it came to light.

Sunday, 5 a.m.: The BART police daily log is sent to more than 500 subscribers, which include members of the media and residents who requested it. It includes three brief items, including a one-paragraph account of the robberies at the Coliseum Station.

Monday, 8 a.m.: The Chronicle is tipped off to the crime and pursues the story. Once the story is posted online, other local media quickly jump on it — and before long, it is the top-read story on local news sites and is attracting national attention.

Bottom line: While BART did not exactly hide the incident, it certainly made no concerted effort to assure that Bay Area residents were aware of it.

Why? Alicia Trost, a BART spokeswoman, said if the crime had resulted in a more significant service disruption or station closure it would have triggered alerts to the media and more immediate inquiries.

“We know it’s big when we work at BART and our friends and relatives start reaching out to us and asking: ‘Is BART safe?’”

Alicia Trost, who insisted the system, which provides 430,000 trips a day, is a relatively safe mode of travel, and that security has been tightened since the Coliseum Station robberies.