Wait a minute, I'm a racist, bigoted, closed minded sexist just because I'm white?
fuckin lol
No. What he's saying is that some, or many, people will assume all that because you're white. I'm a 41 year old white man. In my experience, that's not been true, to my knowledge. But I have seen a "lite" version, which is that people of other races assume I don't know much about what it's like to be hispanic, asian, black, etc. And that's fair to say. Most of what I know about that is from those same people explaining it to me.
Anyway, even if people did assume I'm racist, etc, not only will they soon find out otherwise if they're around me much, but also - there are no significant consequences to me. They'll assume these things in their own mind. It's unlikely that it will turn into action.
For a black man, as an example, there might be physical consequences involved in other people's assumptions about him. I hope I don't have to come up with examples of that.