Our conversations about racism are all wrong
We define "racism" as doing something horrible, like being a member of the KKK, using the N word, making racist jokes, etc. That means that to say someone is doing something racist, we are saying they are a horrible person. We use the word "racist" as a noun because that means that once someone has done or said something racist, we have decided they are horrible people and we dismiss them and everything they ever do as being unworthy of consideration or attention.
But I think that's totally off. Racism is bigger than that. It's a part of our society, and a part of every institution and system, built into them - sometimes intentionally and sometimes unintentionally. And we don't necessarily even see it because it's normal, particularly those of us who are white because it doesn't affect us in the same way.
If we look at racism in this way, we can see that nice and well intentioned people can accidentally say something racist without being "a racist." Without a need to dismiss every other thing they do and say ever. If someone says that Michael Moore put forward a racist idea, that doesn't mean they think he's "a racist" and should be dismissed as horrible and never to be listened to again about anything. It just means he's a privileged white person, just as all white people are, who didn't see the racism because we simply don't always see it. Not because we're bad, but because it's built into our society and just too big, and it doesn't affect us in the same way so we don't have the same response to it.
And if privileged white people accidentally say something racist, we don't have to get defensive. We can recognize that it's just being a part of our racist society and being privileged to not have that racism affect us in the same way, and not something horrible about us. We can learn from it - learn to recognize it better - and grow as people.
I wish we as white people could stop jerking our knees over the word "racism" and accept racism as what it is - something much bigger than one person, or a group of people. Something nice good people who are not "racists" (in the noun sense) can sometimes do accidentally, and that if we do accidentally do it, it doesn't make us bad people. How we should respond is to listen to the criticism of what we said, and learn from it, and try not to get defensive because there's no learning once someone becomes defensive.
But just look at any thread on white privilege on DU if you weren't feeling like your head was hurting enough and needed a reason to feel like banging it against a wall. No matter how well someone explains it, it doesn't matter.