Proof of Facebook's bias from Facebook itself.
"Facebook on Tuesday released the initial report prepared by its external auditor concerning the rampant speculation about anti-conservative bias at the company. More than a year ago, however, company officials privately copped to the fact that they’d failed to properly vet the man chosen to spearhead the effort, according to sources involved in the exchange..."
https://gizmodo.com/facebook-privately-admitted-failure-in-vetting-the-auth-1837412697