"Controversy wins. Negative beats positive. All attention looks good to an algorithm."

FB allows lies and divisiveness, as they attract more eyeballs that FB can sell to advertisers and politicians. 

NYT article

"The company also appears willing to bend its rules for popular conservative influencers. Recent reports by BuzzFeed News and NBC News, based on leaked documents, found that Facebook executives had removed “strikes” from the accounts of several high-profile conservative pages that had shared viral misinformation in violation of the company’s rules."