King's adultery has been well known and talked about for decades. He was trained at a very liberal seminary (I believe it was Union Theological Seminary) and did not believe the Bible was the Word of God or that the blood of Jesus could save anyone. His associations with communists were also known. Same with Jesse Jackson, who was a well known friend of Communist Fidel Castro and one of King's aides. Just look at the Congressional black caucus in Congress: chock full of communists.
Did King do some good? Yes. His protests were peaceful, and he sought to change the social status of black people in America through peaceful protests, which is admirable. But let's not paint King as some kind of saint. He was not. He has no credibility as a man of God.