ZeroHedge and The Federalist have apparently racist comments on their sites and they don't moderate them.
Advertisers don't want to be associated with those comments or have their ads placed on such sites.
Google says "You can say whatever you want but we won't place our advertisers' ads on your sites if you don't clean them up."
If companies wanted their ads to run on those sites I assure you Google would do it.
Is it time for the government to force companies to run ads on every site?
Is Crate & Barrel censoring ZeroHedge if they don't want their ads on a site with racist comments?