If they are taught both sides, they can weight the evidence for themselves. I'm confident they will come to the right conclusion. They are going to hear that sometime in the real world anyway. You and I have. But again, whether that particular crackpot theory needs to be taught depends on the threshold you set. If you set it low enough to pick up Muslim beliefs, it might slip in past the threshold, but I doubt even most Muslims deny the Holocaust.
"That is true. Amongst historians, Holocaust denial is not very common. And amongst scientists, intelligent design has very little acceptance."
Well I think ID has more acceptance among scientists than Holocaust denial has among historians, but again you are forgetting "guided evolution" which the article admits has a much higher following. I say teach or at least acknowledge all three, instead of presenting one and only one side.