Search on Facebook, Twitter, YouTube and Reddit promotes holocaust denial.

This may not be the result of a specific decision by those companies. I've read that Nazis have figured out how to manipulate the data that search algorithms operate on. Even if those companies, or some of them, do not intentionally support right-wing extremism, being its helpless tool is bad too.

I've seen arguments that the tendency of algorithms to promote extremist material — at least on Facebook and Twitter — is because they have been designed to show people things that make them want to stay on the site longer. That relates to the business models that make these sites so harmful in other ways.