Earlier quoted context omitted.
Or Facebook has learned the art of Plausible Deniability. If the bias happens during hiring (by preferring candidates who naturally lean left), then Facebook merely needs to give them curation power without giving explicit instructions.
This sounds too much like a conspiracy theory to take very seriously. Never attribute to malice what you can attribute to incompetence.
http://www.cnbc.com/2015/09/27/angela-merkel-caught-on-hot-m...