I can't believe I'm getting into this discussion but you brought up a good question and I'd like to offer my two cents.
I think that it is possible for a white person to use that word and not be racist. I live in the south so of course I hear that word a lot. But when I hear MOST white people say it, IMO they don't mean it in the context of trying to keep a black person down. In fact, it's the complete opposite. It's usually said about a black person that refuses to work, that sits around the house and collects a check and 





about how white people try to keep them down, doesn't keep their property up, constant in and out, blaring their music. This doesn't apply to all black people. There are lazy people in any race. I know or know of several white people that are shining examples of the description above and I get just as irritated and put-off by their behavior.
Having said that, I in NO WAY condone the "n" word being used in any context, by anyone. As best as I can, I understand how and why that is such an ugly word and black people being majorly offended by it. But if a white person does say it, it doesn't mean he/she is a member of the KKK, flies the confederate flag, etc. I think it's a term to describe general laziness/sorriness.
I hope I didn't offend anyone, I'm just giving my personal perspective and again, I DO NOT condone the use of the "n" word by anyone.