Martin Luther King Jr. cheated his way through college, relying on numerous and massive cases of plagiarism, to the point his doctoral thesis is utterly without value. When this was discovered, his university, his family and many others went to great lengths to try to cover this up. When that failed, they did everything they could in order to downplay it, to the point society at large doesn't know about it, and those who do usually don't know how significant it was.
During the Civil Rights Movement, King intentionally had youths engage in dangerous protests so pictures would be taken of children being assaulted, which he felt would generate better publicity than if it were adults who were assaulted. There is significant reason to question whether this tactic actually helped his cause. Many of King's contemporaries were adamantly opposed to King's practice of intentionally creating violence, especially when those who would get hurt were children.
There's much more that could be said, but my point isn't to say King was a terrible person. My point is this, King was not a great man. He's celebrated today not for the person he was. King is celebrated for a person he never was. Today we celebrate a figure created out of ignorance, self-delusion and outright lies.
Here's my hot take, we would not have this holiday if King had not been assassinated by a white man when he was. His death created a symbol of a black man people could use to signal their opposition to racism.