They have been all over Facebook and Zuckerman over the accusation of slanting the "Trending" column by dropping conservative stories. A Congressional hearing is promised.
Not that I approve, I'm conservative too, but the United States has been blessed with slanted news reporting since the founding of the Republic. Look at the New York Times. In the 1930's they supported Soviet communism. "I have seen the future and it works". In the 1950's they supported Fidel Castro, strongly enough to make him dictator of Cuba. In the 1960's they backed North Viet Nam. They published the Pentagon Papers in order to destabilize the Nixon administration. They published a leak from CIA about tapping Osama bin Laden's satellite phone, result, Bin Laden ditched the phone and went back to messengers.
I don't see much difference between want the Times does and what Zuckerman is accused of doing at Facebook.