The boundaries of discourse

What should be the attitude towards Holocaust deniers? Should they be silenced, or should they also be allowed to offer their wares?
Should open discussion be allowed on this issue as well, or is the fear that uncritical people will fall for their own nonsense?
And if they need to be silenced because of this fear, who decides and how will they decide what issues the masses can fall for?
And maybe the reason for the censorship of such types is different? (If the rabbi supports their censorship)