Then make a rule that bans people for spamming the forum with the same threads over and over. You can setup an official Holocaust Denial thread for people to argue about it there.
This person specifically says they target Holocaust deniers with censorship because they don't feel they should counter that position with evidence and reason. That's a really, really bad strategy.
A much more effective strategy would be to contain the debate within a single thread and get historians to engage these people charitably, but start laying down the evidence.