Tech companies have long argued they are not responsible for the content posted by others on their platforms. Under this view, a tech company is not responsible if someone posts threats to kill others or instructions for building a bomb or details on how to hack into government computers.
Companies have stood behind this principle, especially in regards to users posting defamatory content to online forums. They have argued that they are not responsible for the content and that it would be impossible for them to police the content of their forums.
Now however, the tech companies, including social media companies, are arguing that they can and do police all speech on their platforms. This implies that they do, in fact, control and have responsibility for the speech on their platform. These actions are likely to emerge in future anti-defamation suits filed against online tech firms and they could find themselves liable for all types of infringing speech conducted on their platforms.
Tech companies can certainly condemn offensive speech. But censoring offensive speech puts tech companies into a area that may have legal ramifications.
Related from St. Louis Dispatch:
“A law that can be directed against speech found offensive to some portion of the public can be turned against minority and dissenting views to the detriment of all. The First Amendment does not entrust that power to the government’s benevolence. Instead, our reliance must be on the substantial safeguards of free and open discussion in a democratic society.” — Justice Anthony Kennedy