Some white people think of racism in overly-simplistic terms. Whether they mostly do it purposely or not is anyone's guess. But they seem to not "get" that being racist is a spectrum, spanning all the way from a simple prejudicial thought to the murder of a black person. And falling anywhere on that spectrum is terrible. Just because you don't spend your every waking moment dedicated to hating black people, doesn't mean you aren't racist. Racism is a value; it is taught, applied, and held close by a large number of people.