That's often said, but never proven. However, even if it were proven, he's not known for Marxism but for his work righting horrible wrongs in America. See, you may not want to admit it, but blacks were treated like absolute crap in this country, and MLK was one of those who stood up and did something about it. Unfortunately it cost him his life.
Are you Arlen Specter? Not proven?
R E A D H I S O W N W R I T I N G S !
Was that slow enough for you to understand?
Do you understand Marxism? Would you prefer that I call it socialism?
You can remember him however you like, but his own words betrays his marxist/socialist/communist underpinnings.
And NO!, he doesn't deserve a national holiday no matter what his contributions. And NO!, it doesn't have anything to do with race.