Over time, Malcolm X’s historical reputation has generally improved. This is partly because of changes in his own beliefs and partly because of changes in American society.
In terms of Malcolm’s own beliefs, the major change came when he took his pilgrimage to Mecca. Before that, Malcolm had been a black nationalist to the point of being anti-white. The pilgrimage to Mecca brought him to believe that white people were not evil and that he should be more tolerant. If this change had not happened before he died, his reputation would surely have been much different.
Second, American society has changed greatly in the past 40+ years. Malcolm’s ideas about black nationalism and black pride are no longer seen as so dangerous. In the 1960s, Malcolm seemed like a dangerous radical. Today, his ideas no longer seem as if they might destroy American society. Therefore, he no longer seems to present (in retrospect) as much of a threat to American society as he would have while he was still alive.
For these reasons, Malcolm X is generally seen more positively by historians than he was by his contemporaries.