Amazon was caught selling thousands of items that have been declared unsafe by federal agencies. In response, the company says it uses machine learning and natural language processing to monitor the items it sells.
YouTube, which has more than 1 billion users, has been criticized for not moving swiftly to take down homophobic content and videos denying the veracity of mass shootings at schools. The company has updated its hate speech policies and currently employs 10,000 human moderators.
Facebook has been criticized for failing to adequately moderate both hate speech and calls for genocide of the Rohingya minority Muslim group in Myanmar. And while the company employs human content moderators, that comes with its own set of issues.
Twitter has made policy changes to help curb abuse, but it still has a long-standing white supremacist problem.