On one hand, Daryl Davis is a hero, and his method actually works to de-radicalize people. I prefer using this method when I encounter bigots irl.
On the other hand, allowing bigoted speech in your online platform has the potential to drive away normal folks and turn your platform into the echo-chamber where bigotry flourishes that you mentioned. This is basically what happened to Voat.
I may disagree with what you have to say, but I shall fight to the death to defend your right to say it.
I agree with this, but it's beside the point. This isn't a public space like a street corner, it's a managed public/private space like a bar, where the bouncer will kick you out for abusing other patrons.