re: So fight ideas with ideas.
Normally I would agree with your position, but in this case Adam is right. It is wilfull lying and perversion for political gain. Why would you have to defend and explain yourself if some malicious neighbours started rumours that you or one of your family is a sexual child-predator? The motive of that lie would be purely malicious and would have nothing to do with 'free debate' - and you wouldn't be expected to deal with it as such. Same thing here.
OTOH if it becomes necessary to further publicize and properly document the holocaust as a result of the Irvings and Tobens - then so much the better for future generations. There is always a tendency to forget.