Facebook pays its subcontracted workers very little, and treats them in a way that is cruel if not fraudulent. When they demanded better treatment, the subcontractor told them to shut up or quit.

Subcontracting enables Facebook to disclaim legal responsibility for all of this, but morally Facebook is entirely responsible.

If company A buys goods or services from company B, and none of the workers of B are particularly associated with company A's purchase, there is usually no reason to hold A responsible for how B treats workers. But when B is hired to provide people to work for A, morally speaking they are working for A. We should change the law to match the morality.