No one wakes up one morning and starts denying genocide. Holocaust deniers themselves understand they're engaged in a longer-term propaganda campaign. They don't have to sell the whopping lie upfront. They plant the smallest seed of doubt now; they'll water it later.
This drip, drip, drip of denial is core to their strategy of rehabilitating and legitimizing Nazism as an ideology, towards their goal of winning people over to their agenda of anti-Semitism, racism and hatred. To spread hate and indoctrinate, they exploit platforms that give them any opening.
When Facebook CEO Mark Zuckerberg recently remarked, "I don’t think [Holocaust deniers] are intentionally getting it wrong," adding that only "if a post crossed the line into advocating violence or hate against a specific group" would it be removed, he was playing directly into deniers’ hands.
As historians and moderators of the largest public online history forum, the subreddit AskHistorians, we confront Holocaust deniers every day. Experience has led us to only one possible conclusion: Giving them a voice is playing a game where they make the rules.
It is no coincidence that deniers have been welcomed with open arms in the "post-truth" alt-right community. Deniers depend on the distortion of historical evidence and outright lies. They cry out "Free speech!" and "Open discussion!" when it is caught.
But about this historical period, there is no "if," no "but": Holocaust denial is a malicious movement to stoke hatred and violence. For Internet communities to fight them means denying them the first word, the last word, and any word at all.