(CNN) — An argument between two mothers at my children's elementary school turned ugly recently when one of the moms was told to "go back to where you came from."
"What are you talking about?" replied the horrified woman, who was born in the United States and had an Indian heritage. "I am just as American as you!"
The aggressor doubled down with an even more racist retort.
I heard about the incident shortly after it happened from several other parents who had witnessed the exchange, all of them deeply troubled by the woman's prejudice.
"Did you say anything?" I asked.
No, they each said. None of them had felt comfortable intervening.
This is not particularly surprising. When people in "the majority" use their social privilege to denounce bias, it can have a powerful impact on the psychological well-being of minorities. Yet research shows that majority group members rarely confront explicit or blatant prejudice in person, even when they want to.
Those perfectly articulated and wickedly poignant verbal smack-downs of prejudiced offenders may happen in films and literature but occur far less frequently in real life.
Social psychologist Aneeta Rattan cites three principal reasons for this reticence.
Under fraught circumstances, majority group members who are not usually targeted by prejudice may not even be sure whether something biased has happened. So first, they have to make that determination, says Rattan.
Second, she observes, there is a "standing" issue. That is, even if they are certain that someone was targeted by prejudice, onlookers have to determine whether they have the right to speak up.
And finally, people may have concerns over what to say. They may fear for their own safety or have a general aversion to discussing group memberships and a belief that the best way to avoid mistakes is to assume a color-blind stance.
Rattan believes that social media is a new frontier for communicating support for groups being targeted by prejudice.
The notion of taking to social media to oppose prejudice may be head-scratchingly counterintuitive for those of us who have watched waves of hateful online rants leveled at something as innocuous as a Cheerios ad featuring an adorable tot with a black father and a white mother, or the racist and sexist vitriol directed at the Asian-American chancellor of the University of Illinois who failed to shut down the school for a snow day.
And what about the flap over Coca-Cola featuring multiple American cultures and languages in its "America the Beautiful" Super Bowl ad? I'm not a soda fan, but #BoycottCoke? #Getagrip. #Seriously.
Indeed, admits Rattan, "people talk about all the ways that the Internet's anonymity can lead to more prejudice being expressed online." But a series of studies Rattan undertook with her colleague, the late Nalini Ambady of Stanford University, showed that social media also have the potential to serve as the exact opposite.
Take, for instance, the "It Gets Better" campaign, a powerful grass-roots online campaign focused on providing support to young people targeted by prejudice because they are gay or suspected of being gay.
The online effort, observes Rattan, "was like finding a diamond in the rough. It doesn't just showcase that there are people who want to reach out and express support, but it also shows that there is a context in which people are more open to reaching out in ways we don't see in interpersonal relationships."
Analyzing the 50 most-viewed YouTube video messages from the campaign, which collectively had been viewed more than 15.5 million times, Rattan and Ambady sought to understand the content, complexity and impact of the supportive messages.
Messages from these videos were coded to indicate whether they were communicating support ("I want you to know it gets better"), social connection ("You will find and make new friends who will understand you") or social change ("The attitudes of society will change").
The researchers found that while all the messages communicated support and most communicated a social connection, fewer than a quarter of the messages advocated for social change.
What is fundamentally different about messages of social change is what they may say about the person's willingness to sacrifice something in order to change a situation, observes Ruha Benjamin, professor of sociology at Boston University.
"It says the situation needs to change for all of us. It's about solidarity. It speaks to the impact of inequality on all of us."
Rattan and Ambady also sought to understand how the online support messages were perceived by both those targeted by prejudice and majority group members.
The self-identified LGBTQ study participants reported that the support messages with the most impact were the least frequent: those that conveyed ideas about social change, that things can, should and will get better. Interestingly, the heterosexual participants did not observe a difference between social connection and social change messages.
The difference in perspective occurs between those who are targeted by prejudice and those who are not, observes Rattan.
But prejudice comes at a high cost to everyone. Belonging is a psychological lever with broad consequences for your mental and physical health.
It is well-established that those targeted by prejudice have higher rates of chronic stress, anxiety, depression, substance abuse and suicide.
Excluding people can serve up a lifetime of negative impact, including a diminished sense of well-being and self-control -- even lower IQ test performance. Research by Stanford psychologist Greg Walton shows that a sense of not belonging renders a person both less motivated and less likely to persist in the face of obstacles.
And lest you think that prejudice adversely impacts only minority groups, studies have shown a link between prejudice and depression. Racially prejudiced people can experience stress during even the most routine and benign social interactions with people of color. Chronic stress, in turn, is toxic, associated with a higher risk for a host of ills, including a diminished immune response, heart disease, rheumatoid arthritis and diabetes.
But can the simple act of posting a support message online, even one that goes the extra distance to advocate social change, have any substantial or lasting impact on the tidal wave of damage -- health and otherwise -- wrought by prejudice?
Benjamin is not so sure.
"Virtual solidarity is great," she observes, "but if you find yourself rallying more on Facebook than you are in your own community, then you need to think about that, both in terms of effectiveness and in terms of displacement."
At some point, she says, "You must have some skin in the game." Skin, as in solidarity and sacrifice -- the promise of social change.
I think about that Indian-American mom from school. Had I been there when the fight occurred, would I have put some skin in the game? And how could an online message of support, even one advocating social change, have made any difference to that particular woman?
When pressed about the implications of her research for other minorities, Rattan is qualified, noting the need for further research. But she tells me about a Tumblr that popped up following the verdict in the George Zimmerman trial, called "We are not Trayvon Martin." In it, all sorts of people from different backgrounds posted short messages exposing their "privilege," about how and why in their lives they did not have to address the issues that led to young Martin's death.
It was an expression with far-reaching implications for both those targeted by prejudice and those willing to offer up their privilege to express solidarity in the face of a perceived injustice.
"It was," observes Rattan, "a profound example of intergroup support."