The Anti-Defamation League has claimed that Valve allows "the proliferation of hate" on Steam. 

In a new report – spotted by Eurogamer – the organisation said that it had found over 1.8 million "unique instances" of extremist or hate content across the PC platform. Over 1.5 million users and 73,824 groups had used "at least one potentially extremist or hateful symbol, copypasta or keyword on the platform." 

This includes antisemitic, white supremacy and Nazi iconography and copypasta.  
The ADL added that the Valve apparently doesn't have any public policies regarding hateful or extreme content, though this isn't quite accurate. But there is the small matter of why the Steam firm isn't enforcing this 

"While Steam appears to be technically capable of moderating extremist and hateful content on its platform, the spread of extremist content on the platform is due in part to Valve's highly permissive approach to content policy," the organisation said.

"In rare notable cases, Steam has selectively removed extremist content, largely based around extremist groups publicised in reporting or in response to governmental pressure. However, this has been largely ad hoc, with Valve failing to systematically address the issue of extremism and hate on the platform.

The ADL continued: "Valve needs to make significant changes to their approach to platform governance, both in terms of policy and practice to address the ways in which hate and extremism have proliferated on the Steam platform."