Why do some people degrade and cynically criticize DR. MARTIN LUTHER KING JR.?

I have seen some metropolitan scholars state that he was an unfaithful man, and an opportunist like Spike Lee... I have studied MLKJ's life, philosophies, speeches and standpoints yet I find no faults... He seems like a most remarkable, brave, God-fearing and upright human being and wonderful world Noble Peace Prize recipient and leader. H Rios