Beneath the layers of apologia from the tech bros in charge of these companies, not to mention the hand-wringing over a red herring version of Free Speech, remember that Facebook, Twitter, YouTube, and other social media platforms managed to get rid of ISIS and most Islamic extremist groups very easily. They can get rid of white supremacists and far-right content, too. They just don't want to. I'll let you decide whether it's because they're sympathetic or because it would cut into their revenue too deeply.
Deplatforming works. It forces these people into the dark underbelly of the internet where people have to actively seek them out. And people will. White supremacists will go find the other white supremacists even if they're banned from Facebook. The point is to prevent them from being able to spread their messages to people who aren't already white supremacists. Normal kids using Twitter or watching YouTube videos or whatever.
If it doesn't work, why are these sites so militant about keeping al-Qaeda, ISIS, and other terrorist groups off the sites? If we need a "free exchange of all viewpoints" then let them back on YouTube. If not, then admit that we're picking and choosing because we don't perceive white supremacy as terrorism.