I wholeheartedly disagree with this opinion.
Seeing how he's idealized into an impossible standard for activists today, it's cool looking at the correspondence MLK Jr. got back in the day (http://www.thekingcenter.org/archive/theme/4809). Here are some samples:
> Mr. Young criticizes Dr. King and the black community for their support of heavyweight champion Cassius Clay's refusal to be drafted into the military. He also expresses worry about the quality of black leadership and urges a move from a selfish focus on Negroes only to concern for all people.
> Calling Dr. King "The Trouble Maker of the United States," Mrs. Shaw criticizes Dr. King's methods in the Civil Rights Movement. She argues that a "campaign of love is in order" rather than demonstrations.
> Harl Douglass writes in disgust at the position Dr. King has taken on Vietnam War. As a once full supporter of the civil rights movement, he believes that Dr. King "is somewhat unstable and he has made millions of enemies for the Southern Christian Leadership Conference....." Douglass warns Dr. King and SCLC officials that if they continue to go down the same track they will lose support of white moderates.
The 60s civil rights movement was a classically liberal movement. They were demanding equal treatment under the law. "Civil rights" movements today are usually asking for special treatment. (edit: Just to clarify, I'm referring specifically to the US for this last point)