I guess if one highlights the many things MLK did that were immoral, dishonest, and unpatriotic it makes them racist...racism, the last thing someone throws out when they have lost the argument.
No I just don't see any other reason to bash a dead guy who regardless of what his personal morals may have been did accomplish a lot of good. Unless of course one views his accomplishments as a bad thing.
It's the same thing as bringing up Reagan's character defects everytime he is mentioned or honored. Why not just remember him for the good he did and honor his memory, what would bashing him do other than dismiss the good he did?