Sanchez is on the right track here:
[In regards to the supposite Michelle Obama "Whitey rant"] "The most remarkable thing about this rumor has always been that it somehow kept lurching along like some George Romero extra despite being utterly, completely, I’ve-got-a-Nigerian-bank-account-to-share-with-you unbelievable in about twelve different ways. The Ivy League educated wife of a half-white state senator (Hi Grandma! Hi Grandpa!), speaking fully three decades after the release of Cleopatra Jones, does a 30 minute rant about “whitey” with cameras rolling? Is there any element of this that doesn’t positively shriek “bullshit”? I have trouble fathoming how far gone down the ideological rabbit hole you’d have to be to even listen to it through once without giggling, never mind find it “believable”.
"Update: You know, that’s probably backward. What I should be asking is: What exactly have we heard out of Michelle Obama that makes this believable? There was her Princeton dissertation on race and assimilation, which folks tried desperately to mine for something controversial without much success. There was some utterly unremarkable Democratic boilerplate about “moving bars” that pundits like Hugh Hewitt made a profoundly lame attempt to cast as bitter and anti-American. But what has she said that makes it plausible that she’s actually a modern Malcolm XX?"
"Surveying some of these reactions, looks as though a lot of people regard standard leftish rhetoric that would pass without comment in a John Edwards speech as angry and threatening coming from a black woman. Which does suggest another possibility: Suppose there is some kernel of fact, some ur-tape, back at the source of this game of Chinese whispers. (Can one still say “Chinese whispers”?) If there is, I’ll wager that it consists of some uncomfortable but uncontroversial (or at any rate, true) observations about the history of race in America, in which the word “whitey” does not appear, but which nevertheless sound like racist hate speech to some observers. The reactions to Jeremiah Wright’s inflammatory sermons have, I think, shown that there are plenty of people out there who, above and beyond their antipathy to his incendiary mode of delivery, get extraordinarily touchy about any reminder that this country has a long and relatively recent history of treating black people badly."
Even obviously false rumors can gain traction if they validate someone's world view. The only way to combat that is by thinking, and not just about the rumor, but about your world view. As someone against McCain I could easily fall into thinking that that crap out there about the Viet Cong putting a chip in his head is true. But I think I can still be opposed to McCain and be intelligent at the same time. In fact I'd like to think that being rational is more important that who wins the presidency, but maybe that's just me.