Short diary and more just a thought, but this is my take on the Rudy Giuliani comments. He's not the first person to say things like this. I've encountered it before on Facebook and other places.
When Rudy Giuliani defends his comments against Obama by saying they aren't racist because Obama has a white mother, in essence he is saying "Obama is white". This despite the fact Obama self-identifies as "black". Despite the fact that America defines people who look just like Obama as "black" every single day.
Basically Rudy is saying Obama's own self-image and the perception of society at large don't matter when defining Obama's race. Rudy is dismissing Obama's right to define himself as he sees fit or based on how society treats him and people look at him. Rudy is saying his perception as a white man of privilege matters more than Obama's own thoughts on the matter.
That is the very definition of racism. No one gets to define another person's race, period.