The way races are defined is racist to begin with - that is the point - and the way it is being used to label people is explicitly used to put people down. Obama is "black" and not "white" solely because for a lot of people it is very important to label him black to be able to dismiss him. If people were not racist, nobody would e.g. care if people referred to him as white. Try referring to him even as mixed race, or half-white, and see the racists quickly come crawling out of the woodwork to make sure it is made clear how black he is.

It's a description of someone's skin color and facial features for the most part. It's not fundamentally racist, that's just the main use.

Yeah yeah, that rule of thumb is in the racist area but you can discount it and he's still obviously 'black' as much as the term 'black' has any meaning.