Advertisers are making a big mistake by taking as gospel what people say -- or don't say -- about their products or advertising on social media. Except, of course, when it's United Airlines.

Social media attracts people who feel vehemently about something and also people who just want to join in the chorus. But they don't always reflect majority opinion.

And to make matters worse, it becomes difficult to voice a counter opinion, because the dissenter will be immediately jumped on and torn apart limb by limb. It takes a very brave person to go up against an angry mob.

Maybe that's one reason why so few pundits predicted a Donald Trump victory. Social media is especially good at ridicule, and so most Trump supporters were drowned out. Sure, they talked excitedly among themselves about Trump and how he would change the nation, but those views weren't taken seriously in the mainstream media.

If social media were an accurate indicator of public sentiment, wouldn't the swing to Trump have become evident? Once a bandwagon develops, even one way off the mark, it's extremely difficult to start a counter bandwagon in the other direction. Nobody likes to get shouted down.

Too much silence can mislead, just like too much enthusiasm can. In a new book on the election, "Shattered," journalists Jonathan Allen and Amie Parnes write that Hillary Clinton seemed oblivious to basic facts, such as that Bernie Sanders was resonating in the primary or even that populism was on the ascendancy in the Rust Belt. Why weren't there warnings in social media? Because supporters didn't want to rain on her parade.

Where was social media when Clinton needed it? On the night of the election, "Shattered" pointed out, "A nation of Democrats sat in stunned silence. They hadn't been warned. Hillary hadn't been warned. Even her pollsters had been in the dark, sidelined in favor of an analytics team that insisted she was poised to win."

Clinton's email scandal did damage on several fronts, the authors wrote. "Beyond giving caucus-goers pause and hampering her volunteer recruitment efforts, the scandal appeared to tap down the willingness of Hillary supporters across the country to lobby friends on Facebook and followers on Twitter. 'There's a cost to supporting Hillary,' one of her aides said. The email issue 'made it weird and costly for people to be for her.' "

That brings us to social media's recent involvement with the Kendall Jenner Pepsi commercial.
The ad, of course, was fraught with danger at a time when police clashes with Black Lives Matter demonstrators had everybody on edge. The idea was "to project a global message of unity, peace and understanding," but that backfired as social media commenters said the commercial trivialized real-life brutality.

Bernice King, the daughter of Martin Luther King Jr., also drew the connection to protests of another era. She tweeted: "If only Daddy would have known about the power of Pepsi."

All good and powerful points. But a survey of 2,200 adults conducted by a firm called Morning Consult (a Washington, D.C., company whose Obamacare sign-up poll The Washington Post published and whose Brand Index division has partnered with Fortune, Bloomberg News, Politico and Vox) showed that nearly half of respondents had a more positive opinion of Pepsi after watching the commercial. Specifically, 44% regarded the brand more favorably versus 28% who didn't seem to care and about 25% who thought more negatively of the brand.

I admit that you can't dismiss negative views, especially among key demographics. A quarter of those age 18 to 49 said they had a less favorable view of Pepsi after the commercial versus half who had a more favorable view. But who knows, maybe a good chunk of the less favorable were Coke drinkers who were looking for a reason to bash Pepsi.

I'll bet that if social media were up and running when Coca-Cola's "I'd Like to Buy the World a Coke" hilltop commercial aired, it would have been shouted down by social media.

Pepsi said its ill-fated commercial was "trying to project a global message of unity, peace and understanding." The Coke commercial, which ran in 1971 when the Vietnam War was raging, had the same intention. Did Coke "trivialize" the troops killed in Vietnam or the protesters who opposed the war by bringing together a bunch of kids who sang on a hill?

I'll bet social media would have ranted that Coke took a perfectly good song about growing "apple trees and honey bees and snow-white turtle doves" into a crass pitch to sell fizzy water.