I was asked a related question during an interview at Google. As an example, the interviewer told me of a time their ads drew an especially vile reaction: they had placed luggage ads on a news story about a serial killer who chopped up his victims bodies and stuffed them into suitcases.

The interviewer said they'd be happy to just not show any ads on such pages and asked me how I'd go about detecting them. Apparently they've (mostly) figured that out by now!