Did you watch all of it? You basically just outlined his exact point.
He was saying let them speak so we can publicly debunk the ideas, not to legislate against them and try to shut them up entirely, because that makes them more attractive to conspiracy theorists.
He also referred to them as Holocaust Revisionists.
Usually I don't like it when people laugh and scoff about a conspiracy theory, because that just fuels the conspiracy theorists common narrative which is that people won't debate them, they just mock, no factual discussion. But I think this guy is qualified to do that considering he spent literally years researching and debunking the theories.