I have not heard about Mr. King warning against white liberal but Malcom X did...
“The white liberals, who have been posing as our friends, have failed us. The white liberal is the worst enemy to America and the worst enemy to the black man.”
“White liberals are those who have perfected the art of selling themselves to the black man as our ‘friend’ to get our sympathy, our allegiance and our minds. The white liberal attempts to use us politically against white conservatives, so that anything the black man does is never for his own good, never for his advancement, never for his own progress, he’s only a pawn in the hands of the white liberal.”
White Liberal and Dems took LBJ's words to heart and acted on it.. "I'll have those N-word voting Democrat for the next 200 years", "These Negroes, they’re getting pretty uppity these days and that’s a problem for us since they’ve got something now they never had before, the political pull to back up their uppityness. Now we’ve got to do something about this, we’ve got to give them a little something, just enough to quiet them down, not enough to make a difference." - LBJ. Johnson called the Bill of Rights as the "N-word Bill".