It is worth noting that some of the censorship of Nazi/Fascist ideas can be traced back to laws imposed by the Allies after WW2:

http://en.wikipedia.org/wiki/Denazification#Censorship_in_th...

Once these kind of rules get put in place what politician is realistically going to ask for them to be repealed?

[Personally, I would leave these laws in place while there are people alive who suffered directly from the Nazis].