Martin Luther King Jr. is cherished by most Americans, treated as one of the greatest peaceful protesters in history, and heralded for bringing people together to help combat racism in the US.

But it wasn't always this way.

Back in the 1950s and 1960s, King was repeatedly derided by his opponents for inciting violence. The FBI even investigated him, fearing his potential impact on US society. The White House, meanwhile, seriously feared that the March on Washington would lead to riots and violence — something that seems completely absurd today.

Still, we see something similar today in how the public and media behave toward people they disagree with, from the Tea Party to the Black Lives Matter movement. This is why the history of King's treatment matters: It shows just how easy it is to misread and demonize the intentions of people we disagree with, even when it involves someone now widely considered an American hero in peaceful protest.

Martin Luther King was criticized for inciting "hatred and violence"

King, who's now widely seen as an advocate for peaceful protest, wasn't quite viewed that way by everyone during the 1950s and 1960s.

A 1963 letter from eight white clergymen — which inspired King's famous response, "Letter From a Birmingham Jail" — told black protesters to stand down because they were inciting "hatred and violence" in Birmingham, Alabama. The clergymen warned about the effects the protests in Birmingham led by "outsiders" like King would have:

Just as we formerly pointed out that "hatred and violence have no sanction in our religious and political traditions," we also point out that such actions as incite to hatred and violence, however technically peaceful those actions may be, have not contributed to the resolution of our local problems. We do not believe that these days of new hope are days when extreme measures are justified in Birmingham… We further strongly urge our own Negro community to withdraw support from these demonstrations, and to unite locally in working peacefully for a better Birmingham. When rights are consistently denied, a cause should be pressed in the courts and in negotiations among local leaders, and not in the streets. We appeal to both our white and Negro citizenry to observe the principles of law and order and common sense.

These fears of King's tactics and rhetoric went all the way to the White House. While many now know of the March on Washington in 1963 — in which King gave his renowned "I Have a Dream" speech — as a peaceful event, the Kennedy administration at the time expected the absolute worst. Pointing to the occasional violence among some of the civil rights protests swarming the country, critics and skeptics worried that the march would turn into a huge race riot.

President John F. Kennedy's brother and then-US attorney general, Robert Kennedy, invoked many of these fears in justifying what amounted to a preparation for war in DC. According to Nick Bryant of BBC News, Robert Kennedy told his brother during a tense White House meeting, "Negroes are now just antagonistic and mad and they're going to be mad at everything. You can't talk to them. My friends all say [even] the Negro maids and servants are getting antagonistic."

"NEGROES ARE NOW JUST ANTAGONISTIC AND MAD AND THEY'RE GOING TO BE MAD AT EVERYTHING"

As Bryant reported, these types of warnings were taken so seriously that the federal government essentially mobilized all its resources to prepare for the worst, deploying troops, beefing up security, ramping up surveillance, and clearing jails for new arrests. "The mission went by the code-name Operation Washington," Bryant explained. "So heavy was the military build-up that one reporter observed that 'the city was transformed from the capital of a nation at peace to a nation at war.'"

After the peaceful march and speech, the FBI continued describing King as a possible national security threat. William Sullivan, then-head of the FBI’s domestic intelligence division, wrote in a 1963 memo:

Personally, I believe in the light of King's powerful demagogic speech yesterday he stands heads and shoulders over all other Negro leaders put together when it comes to influencing great masses of Negroes. We must mark him now, if we have not done so before, as the most dangerous Negro of the future in this Nation from the standpoint of communism, the Negro, and national security.

In retrospect, these types of warnings and preparations seem ridiculous. The march and King's speech are now viewed as part of the most successful peaceful protests in US history, leading to significant changes like the Civil Rights Act of 1964 and the Voting Rights Act of 1965.

But this is actually all too typical of how people treat others whom they disagree with.

We tend to demonize groups we don't agree with

People often see the worst in those they passionately disagree with. By many measures, this is getting worse in our current political environment: As Vox's Ezra Klein wrote, Americans are now much more likely than they were in the past to discriminate against each other based on political party affiliation.

Americans have seen this in modern protest movements. Conservative defenders of police wrongly characterize the Black Lives Matter movement as violent, based on the actions of a few people within the movement. Similarly, liberals have blamed the Tea Party movement for inspiring right-wing extremism — even terrorism — and anti-abortion groups for causing violence against women's health clinics.

It is useful to see why certain causes inspire violence. For example, by looking at why people rioted in Baltimore following Freddie Gray's fatal injury while in police custody, I found a very convincing case that people were genuinely angry, and rioting was the result of decades of neglect. So perhaps instead of just demonizing the violence, it might be more useful for political leaders to heed the root causes — and not dismiss the complaints of largely ignored, downtrodden communities in the future.

But people sometimes take these types of analyses too far, using them to decry whole movements based on the actions of a few. That happened in the past year when Fox News called Black Lives Matter a "hate group," and when pro-choice groups said Carly Fiorina's anti-abortion rhetoric led a man to shoot up the Colorado Springs, Colorado, Planned Parenthood clinic. And it happened decades ago when the FBI considered King a national security threat because some civil rights protesters acted out violently.

As Kevin Drum, a blogger at Mother Jones, wrote:

People and groups have to be free to condemn abortion or police misconduct or anything else — sometimes soberly, sometimes not. And it's inevitable that this will occasionally inspire a maniac somewhere to resort to violence. There's really no way around this. It's obviously something for any decent person to keep in mind, but it doesn't make passionate politics culpable for the ills of the world. We can't allow the limits of our political spirit to be routinely dictated by the worst imaginable consequences.

King exemplified this issue. He's now widely viewed as a pioneer in peaceful protest. Yet because of his passion, and how a few people violently interpreted his cause, he was accused of inciting violence and treated as a threat by the federal government.

That obviously seems absurd today. But it offers a good lesson: Maybe it's worth thinking about how accusing largely peaceful modern movements of inciting violence could look 50 years from now.