Not only that, companies like Twitter, Facebook, Google and Microsoft have full time people dedicated to dealing specifically with illegal content. They don't have many full-time employees (they can't as these positions often require very specific contracts with the Department of Justice for handling this type of evidence) which has resulted in at least two cases of employees sustaining pretty bad mental health problems:
http://mashable.com/2017/01/13/microsoft-employees-sue-ptsd-...