Every new generation is a blank slate that must be educated all over again.
You and I are of the generation that has studied the sum of the historical facts and have convinced ourselves of what really happened and can defend our position.
However, once new generations are told, "This is so because we say so and you are not even allowed to question what we say or you will be jailed", that passes into the realm of dogma which threatens the credibility for future generations.
For example, was the beginning of the "The Diary of Anne Franke" actually written by a 13 year old girl? (That's a trick question that requires some research in order to arrive at the correct answer.)
To criminalize such questions casts doubts on the authenticity of the entire work in the minds of future generations and defeats the work itself.
Those questions aren´t criminal. But saying "Did the Holocaust happen at all, or have we all been betrayed by our filthy government and the Jewish lobby?" surely is.