The politics and polling website FiveThirtyEight had an article about the contemporary and retrospective popularity of various protest movements called, “The NFL Protests May Be Unpopular Now, But That Doesn’t Mean They’ll End That Way”. The big take-away is “civil rights movements, almost by definition, begin unpopular.”
Here’s the section about King specifically:
Marches for civil rights during the 1960s were generally seen negatively at the time. As Washington Post noted last year, most Americans didn’t approve of the Freedom Riders, the March on Washington in 1963 or other similar protests. In fact, many Americans thought that these protests would hurt the advancement of civil rights. In addition, but many Americans held mixed-to-negative views of civil rights leader Martin Luther King Jr. In a 1966 Gallup survey, 63 percent of Americans gave King a negative score on a scale from -5 to +5. Now, the civil rights marches are viewed as major successes, and just 4 percent of Americans rated King negatively on that same scale in a 2011 Gallup poll.
That linked Washington Post article also adds:
In 1965, two years after the March on Washington, 94 percent of African Americans rated the job Martin Luther King Jr. “has done in the fight for Negro rights” as positive, according to a Harris survey.
But when the polling company asked white adults the next year whether King was helping or hurting the cause, just 36 percent said he was helping; half of whites said he was hurting, while 14 percent said they weren’t sure.
That I think gets to one of the core issues: King was view unfavorably by White Americans (and therefore most Americans overall), but was view very favorably by Black Americans who, if anything, had the opposite criticism of him from White Americans. From that same WaPo article:
African Americans in the 1960s debated the movement's tactics and strategies. While 71 percent of black adults in a 1963 Gallup poll said King was moving at the right speed, 21 percent said he wasn’t moving fast enough. Indeed, defining what it meant to act with “all deliberate speed” was “a big, big deal,” Cox said.
One interesting thing to note, that you can see if you click through to the Gallup poll linked above, is that public opinion of King was growing more unfavorable in the years between the 1963 “I Have a Dream” speech and the March on Washington and his assassination in 1968 (Gallup actually didn’t poll through 1968, or if they did it’s not included in this document, so we have polling only through ‘66—I imagine the trend continues but I’m not sure).
| Date | Highly Favorable (+4, +5) | Highly Unfavorable | Total Favorable (+1 to +5) | Total Unfavorable |
|---|---|---|---|---|
| Aug, 2011 | 69 | 1 | 94 | 4 |
| Aug, 1966 | 12 | 44 | 33 | 63 |
| May, 1965 | 20 | 31 | 45 | 46 |
| Aug, 1964 | 16 | 25 | 44 | 38 |
| May, 1963 | 16 | 25 | 41 | 37 |
You can clearly see his popularity was declining and his unfavorability ratings increasing during the the 1960's. The only polls I could find (using the Roeper Center's iPoll database) from 1967 and 1968 looked at King's popularity on specific issues, but they continue to paint him in a similarly unpopular light.
A 1967 Harris Poll asked, "Do you think by his coming out against the war in Vietnam, Martin Luther King is helping or hurting the civil rights cause or don't you think it will make much difference one way or the other?" 3% said helping, 57% said hurting, 27% said no difference, and 10% said not sure. (Per polls in the 1970's and later, King sped up civil rights, though this poll is about the very specific issue of Vietnam and may not necessarily reflect broader opinions of King.)
The Religion and Civil Rights survey, also from 1967, asked respondents whether "Martin Luther King is an outstanding example of making Christianity relevant and meaningful for our day". 35% said definitely disagree, 28% probably disagree, 24% probably agree, 14% definitely agree. Total disagree was 63%, total agree was 38% which is probably a decent proxy for his overall favorability (not much change from the 1966 Gallup poll).
As with many public figur s, after his death he started becoming slightly more popular, but still, it's not as if this magically made him more popular. A NORC poll from April 1968 asked respondents "When you heard the news of the assassination of Dr. Martin Luther King, Jr., which one of the things listed on the card was your strongest reaction?" and then were given a set options. 38% said Sadness, 5% Anger, 15% Shame, 10% Fear, 31% Felt he brought it on himself, 1% Don't know.
I found no opinions about his favorability or unfavorability ratings in in the 1970's (most of the polling in the 70's was about whether his assassination was the result of a conspiracy, to which most respondents said yes, it was--a poll in the 1990's found a similar result), but by the 1980's, his support was close to current levels. An ABC News/Washington Post Poll from 1986 found that 97% had favorable, 1% had unfavorable views of King. A People, The Press & Politics Poll from 1987 found him to have slightly lower favorability ratings (29% Very favorable, 45% Mostly favorable, 14% Mostly unfavorable, 6% Very unfavorable).