Holocaust denial may be compared to either the match or the fuel for a feared conflagration that could again consume Europe, and all the smoky points short of that.
Lets compare the denial to a spark , and the anti-semitic attitude to a fuel vapor , can I compare the forbidding of certain ways of thinking to the containment vessel of the spark and fuel that will make the resulting explosion brisant?
Holocaust deniers seem stupid when they are surrounded by reliable evidence that is easily found and difficult to deny.
But to forbid them from saying what they want lends a sort of credibility to them that they haven't earned.
As a technique for preventing a conflagration ,this one is weak.
Another metaphor might be the small boil that needs lancing , it is not really good to prevent the gush of noxious puss , youmight get a lot more puss later in a bigger boil more painfull to lance.
Europe can't solve its problems with anti-semitism by stifling the freedom of expression , it does nothing to persuede the wrong thinking people , even if it may hide the puss a little while.